ArticlePDF Available

Visual Realism Enhances Realistic Response in an Immersive Virtual Environment - Part 2

Authors:
Insu Yu
Insu Yu
Insu Yu
  • This person is not on ResearchGate, or hasn't claimed this research yet.
Jesper Mortensen at University College London
Jesper Mortensen
Pankaj Khanna
Pankaj Khanna
Pankaj Khanna
  • This person is not on ResearchGate, or hasn't claimed this research yet.
Mel Slater at University of Barcelona
Mel Slater
Download full-text PDF
Read full-text
Download citation

Abstract

Does realistic lighting in an immersive virtual reality application enhance presence, where participants feel that they are in the scene and behave correspondingly? Our previous study indicated that presence is more likely with real-time ray tracing compared with ray casting, but we could not separate the effects of overall quality of illumination from the dynamic effects of real-time shadows and reflections. Here we describe an experiment where 20 people experienced a scene rendered with global or local illumination. However, in both conditions there were dynamically changing shadows and reflections. We found that the quality of illumination did not impact presence, so that the earlier result must have been due to dynamic shadows and reflections. However, global illumination resulted in greater plausibility - participants were more likely to respond as if the virtual events were real. We conclude that global illumination does impact the responses of participants and is worth the effort.
Content uploaded by Mel Slater
Author content
All content in this area was uploaded by Mel Slater
Content may be subject to copyright.
T

#%
 $&&-)$"#!#% $ -).)  -)%#,-)/
-"#% %!!"&%# ) '#$%(!! ! )
.!#$)#)
/+ '#$%(!#! )&%(!$(!!()#! )" *

N*-- .+*)$)"0/#*-= ''/ -<( '.'/ -Q0> 0

* .- '$./$'$"#/$)"$))$(( -.$1 1$-/0'- '$/4++'$/$*) )#) +- . ) <
2# - +-/$$+)/.! '/#//# 4- $)/# . ) ) #1 *-- .+*)$)"'4@0-
+- 1$*0. ./04 $)$/  /#/ +- . )  $. (*-  '$& '4 2$/# - '?/$(  -4 /-$)"
*(+- 2$/#-4./$)"<0/2 *0')*/. +-/ /#  !! /.*!*1 -'',0'$/4*!
$''0($)/$*)!-*(/# 4)($ !! /.*!- '?/$( .#*2.)- !' /$*).> - 2 
 .-$ ) 3+ -$( )/2# - US+ *+'  3+ -$ ) . ) - ) - 2$/#"'*'
*-'*'$''0($)/$*)>*2 1 -<$)*/#*)$/$*)./# - 2 - 4)($''4#)"$)"
.#*2. ) - !' /$*).>   !*0)/#//# ,0'$/4 *! $''0($)/$*)$)*/ $(+/
+- . ) < .* /#/ /#  -'$ -- .0'/ (0./ #1   ) 0  /* 4)($ .#*2. )
- !' /$*).> *2 1 -< "'*' $''0($)/$*) - .0'/  $) "- / - +'0.$$'$/4 ?
+-/$$+)/. 2 -  (*-  '$& '4 /* - .+*) . $! /#  1$-/0' 1 )/. 2 -  - '>  
*)'0 /#/ "'*' $''0($)/$*) * . $(+/ /#  - .+*). . *!+-/$$+)/.) $.
2*-/#/#  !!*-/>

! 
Virtual environments, presence, visual realism, real-time global illumination, shadows,
reflections, virtual body, avatar.

) /#$. -/$'  2  *).$ - /#  $(+/ *! - '$./$ $''0($)/$*) *) A+- . ) B $)
$(( -.$1  1$-/0' - '$/4 HI< *)/$)0$)" 2*-& !$-./ - +*-/  -/ T JTK> )
+-/$0'- 2  *).$ - 2# /# - $''0($)/$*) - '$.( $) $/. '! *)/-$0/ . /*
+- . ) < *- 2# /# - /#$. $. *)'4  0.  - '$./$ '$"#/$)" '.* $)'0 . 4)($
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
U
!! /..0#. #)"$)" .#*2. ) - !' /$*). . /#  +-/$$+)/(*1 .-*0)
/#  . ) > $-./2  -$ !'4 *).$ - /# )*/$*) *! +- . ) <) /# ) .-$  /# 
) 2 3+ -$( )/$) /$'>0//$)"/*" /# -/# - .0'/.*! /#  ) 2 3+ -$( )/2$/#
/#*.  *! -/ T< 2  --$1  / /#  *-$"$)''4 0) 3+ /  *)'0.$*) /#/ $) 
- '$./$'$"#/$)")4)($ !! /.- */#$(+*-/)/*)/-$0/*-. /* +- . ) <
/#*0"#!*-$!! - )/- .*).>
 *+'  3+ -$ )$)"  (4 #1  /#  $''0.$*) *!  $)" $) /#  1$-/0' +' < )
*). ,0 )/'4--4*0//$*)..$!/# .$/0/$*))1 )/. +$/  2 -  - ''4
#++ )$)"> # .  /$*). (4 $)'0  )*)?*).$*0. *) .< $)'0$)" #)" . $)
+#4.$*'*"4 .0# . # -/-/ < #1$*-' *) . .0# ..($'$)" /  1$-/0'#0()
#-/ -< /#-*0"# /* #*2 /# 4 ! ' (*/$*)''4< ) /#  /4+ . *! /#*0"#/. /# 4
#1 >#$.. )./$*)*! $)"$)/# 1$-/0'+' <*+ -/$*)'$5 4/# - .+*). /*
/# 1$-/0' )1$-*)( )/.$!$/2 - - '<$.- ! -- /*."$% <*) +/2$/#
'*)" #$./*-4 2$/# -**/. $) / ' *+ -/*- .4./ (.< .  JUK> #/ $. *! $)/ - ./ /*
+-/$/$*) -.$)/# !$ '< ) ++'$/$*)0$' -.<$./*0) -./)#*2 /#  /0'
+-*+ -/$ .*!/# 1$-/0'- '$/4.4./ (0. (4$)!'0 ) /# . )./$*)*!+- . ) 
*!)1 -" +-/$$+)/>
) *1$*0.!/*- /#/!-*(*((*)?. ). +*$)/*!1$ 2 *0"#/ /**)/-$0/ /*
+- . ) $.#*2- '/#  +$/ . ) '**&.># - - ()4+*..$' ( )$)"./*
A- 'B< 0/ # -  2  *) )/-/  .+ $!$''4 *) $''0($)/$*) - '$.( ? )*).$ -
#*2 (0# * . /#  - '$.( " ) -/  4 /#  $''0($)/$*) (* ' 0.  $) /# 
- ) -$)"*!/# . ) *)/-$0/ /*+- . ) @
)/# ! *!$//# ).2 -2*0'. (/* *1$*0.?$!+- . ) $.*0/+ *+' 
- .+*)$)" - '$./$''4 /*  1$-/0' )1$-*)( )/ . )-$*< /# ) /#  (*-  /# 
$''0($)/$*) *)!*-(. /* - '$/4 /#  (*-  '$& '4 $/ $. /#/ /# 4 2$'' - .+*)
- '$./$''4>*2 1 -<.0-+-$.$)"'4<.*( +.//* .)*/.0++*-//#/1$ 2+*$)/>
 #1 *1 -  /#$. $..0  $)  /$' $) -/ T*!/#$.-/$'  JTK< 0/ 2  - ''*) 
3(+' >$((*).))/ -!-*(#+ '$''JVK--$ *0/) 3+ -$( )/
2# -  +-/$$+)/. # 3+ -$ )  *)  *! !$1  $!! - )/ /4+ . *! $''0($)/$*)
- ) -$)"<-)"$)"!-*(2$- !-( /*-$*.$/4<$)/# A+$/-**(B )1$-*)( )/># 
+$/-**($.2# - +-/$$+)/. )/ -1$-/0'-**(/#/#.+- $+$ 0/*0/$)$/.
 )/ -<2$/#.$")$!$)/-*+/*)*/# -!'**- '*2>H "1 -$ !#$./*-4*!/# 
+$/ -**( )1$-*)( )/ $) -/ T *! /#$. -/$' I>  .0- . *! +- . )  2 -  4
,0 ./$*))$- )'.*# -/-/ #)" .$)- .+*). /*/# +*..$' ./- ..0. 
4/# +- $+$ >/2.!*0)/#//# - 2 - )*$!! - ) .$).0% /$1 .*- *-$)
+#4.$*'*"$' - .+*).  /* /#  $!! - )/ $''0($)/$*) /4+ .= 2$-  !-(  - ) -$)"
+-*0  /#  .(  - .0'/ . -$*.$/4> *2 1 -< 0) - '' $''0($)/$*) /4+ .
+-/$$+)/.#)$)- . $)# -/-/ 2# )/# 4 )*0)/ - /# +$/># - 2.
+- . ) <0/$/2.)*/- '/ /*/# /4+ *!$''0($)/$*)0. >
)-/T*!/#$.-/$' 2  .-$ ) 3+ -$( )//#/'.*0/$'$5 1 -.$*)*!/# 
+$/-**(JTK>)/#/ 3+ -$( )/2 *(+- +- . ) $). ) $''0($)/ 4
-4./$)"( /#**!$''0($)/$*)2$/#/# .( . ) $''0($)/ 4- '?/$( -4
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
V
/-$)">)-4./$)"*)'4 *)  -4 $./- !-*(/# 1$ 2+*$)/$)/*/# . ) !*-
1 -4 +$3 ' H*- .0?+$3 'I ) /#  $''0($)/$*) $.  / -($)  .*' '4 4 /#  $- /
'$"#/ !! / *) /#  !$-./ .0-!  $)/ -. /  4 /#  -4> ) -4 /-$)" /#  !$-./ -4
/#-*0"# /#  +$3 ' !*''*2.  .0. ,0 )/ +/#  / -($)  4 .+ 0'- .0-! .< .*
/#/ $/ $. - !' /  !-*( ($--*- .0-! .< ) $)'0 . .#*2 -4.>  )  -4
./$)" - .0'/. $) '*' $''0($)/$*) !! /. *)'4< 2$/# )* .#*2.< 2# - . -4
/-$)"- .0'/.$)+*-/-4' *! '$"#/ $)/ -?- !' /$*)  /2 ) .+ 0'-'4- !' /$)"
.0-! .)'.**!#$"#'$"#/.)- !' /$*)./#/4)($''4#)" *-$)"/*
/# # +*.$/$*))"5 $- /$*)*! /#  +-/$$+)/> #  +-/$$+)/. + - $1 
/#  . )  /#-*0"#  # ?/-&  ./ - * # ?(*0)/  $.+'4 ) /# 4 2 - 
)*2 2$/#.$(+' 1$-/0'*4>$) /# -4/-$)"2. 3 0/ $)- '/$( 
/# $-1$-/0'*4/# - !*- ./.#*2.)- !' /$*).$)/# -4/-$)". /#/
(*1 ./# 4(*1 >#$.( )/<!*- 3(+' < /#/ . /# 4 '**&  *2) $)/* /# 
+$/ /# 4 2*0' .   .#*2 *! /# $- 1$-/0' *4 (*1$)" . /# 4 (*1 > # 
!0)( )/'$./$)/$*)</# - !*- < /2 )/# -4./$)")-4/-$)"( /#*.
2. /#/ /#  '// - +-*0  4)($ $''0($)/$*) !! /. H- '?/$(  (*1$)"
.#*2.)($--*-- !' /$*).I)/# !*-( -#)*.#*2.*-- !' /$*)./''>
)/#/ 3+ -$( )/+- . ) 2. .. .. /#-*0"#,0 ./$*))$-  )+#4.$*'*"$'
- .+*). ./* $)"$)/# +$/-**(>/2.!*0)/#/*/#+- . ) ,0 ./$*))$- .
) +#4.$*'*"$' - .+*). . $)$/$)" )3$ /4 2 -  #$"# - !*- /#*.  2#*
3+ -$ ) /# -4/-$)"*)$/$*)> ) <$) / -(. *! +- . ) < /#  -4 /-$)"
( /#*++- )/'4+-*0 /#  // - !! />
 .0.+ / /#/ /#$.- .0'/2.0  /*/# 4)($)/0- *! /#  $''0($)/$*)$)
/#  -4 /-$)" *)$/$*) ? .+ $''4 /#  !/ /#/ /#  (*1$)" .#*2. )
- !' /$*). 2 -  0. 4 ) *-- '/  2$/# #  ) *4(*1 ( )/. *!/# 
+-/$$+)/.>*2 1 -<2 *0')*/-0' *0//# +*..$$'$/4/#/$/2./# *1 -''
#$"# - $''0($)/$*) ,0'$/4 *! /#  -4?/-  )1$-*)( )/ /#/ '  /* /# 
.$")$!$)/'4#$"# -+- . ) $)/# -4/-$)". > ( ( -/#//# -4/-$)"
)*/*)'4#4)($''4#)"$)"- !' /$*).).#*2.<0/%0./!-*(/# .//$
+*$)/*!1$ 2/# $''0($)/$*)2*0'++ -/* (*- - '$./$>
)/#$.++ -2  .-$  ) 3+ -$( )/ /#/2. .$") /*. //' /#$.$..0 ?/*
 / -($)  2# /# - /#   // - - .0'/ !*- -4 /-$)" 2. 0.  4 *1 -''
$(+-*1 ( )/ $) ++ -)  *- 4 /#  4)($ #)" .> .  !*-  2  #1 
*(+-  +- . )  $)  1$-/0' -**( 0) - /2* *)$/$*). 0/ 2# -  !& 
* %!)% $&! %> ) *)  *)$/$*) /#  -**( 2. $''0($)/  0.$)"
./)-+ )*0-0$)/ -+*'/ .#$)"0/$)'0$)"4)($''4#)"$)"
.#*20(-.)- !' /$*).>)/# . *)*)$/$*)$/2.- ) - 2$/#"'*'
$''0($)/$*)< /#/ *! *0-.  # .*!/ .#*2. ) ($--*- - !' /$*).< 0/ '.*
$)'0 */# - "'*' $''0($)/$*) !! /. .0# . *'*-' $)"> $)  /# -  2 - 
4)($#)" .$) */# *)$/$*).<  * $    $%'&)!''%!*&!
&!($#'&*!&' &! >
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
W
#/2  3+ / /*!$)$./#//# - 2*0' )*$!! - ) $)+- . )  /2 )
/# . /2**)$/$*).<.$) /# 4)($ .+ /.*!/# $''0($)/$*)2 - /# .( >
#$.2*0'( )/#//# *1 -'',0'$/4*!/# $''0($)/$*)$.)*/-$/$'!/*-/*
#$ 1  +- . )  0/ /#/ 4)($ #)" . /* /#  $''0($)/$*) ? / ' ./ /#*. 
0. 4 /#  +-/$$+)/B. *2) (*1 ( )/.< 2*0' -$/$'>H#$. ..0( . /#/
/# ++'$/$*)$/. '!$.)*/$)/-$).$''4*0)0+2$/#/# $..0 *!$''0($)/$*)<.$/
2*0' $)/# . *!-#$/ /0-'2'&/#-*0"#++'$/$*).I>
$"0- TG1 -1$ 2*!/# . ) ># .$5 *!/# 1$-/0''$--42.#*. )/*
*$)$ 2$/#/# +#4.$'.$5 *!/# 1 .4./ ($)2#$#$/2.$.+'4 >


 $(+' ( )/ )--$ *0//#  3+ -$( )/*0/0.$)" X'0./ --$1$)"
!*0-2''-$( ).$*) *1 ?'$& .4./ (>H ) !*-/#<2  - ! -/*/#$.0.$)"
/# " ) -$)( A1 BI>#2''2...$")  $/ !*-- ) -$)")
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
X
.$)"' (./ -2.*'' /$)" / ) -0))$)" /#  .$(0'/$*)> # -$( ).$*)
 /*-.4./ ( #. /#-  V( _U>U(&?+-*% / .- ).= !-*)/<' !/<)-$"#/<
)V(_V(!-*)/+-*% /$*).0-! *)/# !'**-># *(+0/ -.$)/# '0./ -
*)/$)  )/ '  )/$0( V>U 5 +-* ..*-. 2$/# T "$"4/  *!  ) 1$$
0-*XYSS"-+#$. -.> #  +-/$$+)/. 2 -  !$//  2$/#.#0// -"'.. .
/#/ 2 -  .4)#-*)$5  2$/# /# +-*% /*-.  '$1 -$)" /$1  ./ - */ WX5 #
4 >//# /*/# /*+*!/# "'.. .2.))/ - ). ?\SS/-&$)" 1$ /*
/-&/# # *!/# +-/$$+)/>
HI2$/#/# (' 1/-
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
Y
HI2$/#/# (' 1/-
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
Z
HI2$/#/# ! (' 1/-
$"0- UG# . ) - ) - 2$/#HI/# ( /#*)HI/# ( /#*
.#*2$)"/# (' 1/-)HI/# ! (' 1/->4)($.#*2.)
- !' /$*).*!/# *4- .#*2)$)''<0/HI)HI#1 *1 -''"'*'
$''0($)/$*))HI*)'4'*'$''0($)/$*)>

# . ) 2 0. !*-/#  3+ -$( )/$..#*2)$)$"0- T># 1$-/0' )1$-*)( )/
 +$/   '$--4 2$/# !0-)$/0- < .*(  **&.# '1 . )  '-"  ($--*- *1 - 
!$- +' > #-  -  '$"#/ .*0- . $''0($)/  /#  . ) >2* 2 -  *) /*+*! /# 
**&.# '1 . +*$)/$)" 0+ ) )*/# - 2. +*.$/$*)  *++*.$/  /# ($--*- *) /# 
&2''>
   .$")  /#  1$-/0' -**( /*   /#  .(  .$5  *! /#  1 < .* /#/ $/. 2''.
*$)$ 2$/#/# 1 2''.># -**(2.*-$ )/ .*/#//# ($--*-2.*)/# 
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
[
& 2'' *! /#  1 < $> >< /#  *)  /#/ +-/$$+)/. 2*0' )/0-''4 !  2# )
)/ -$)"$)/*/# 1 >
$"0- VG#*/*"-+#*!+ -.*)$)/# 1 .4./ (<2$/#/# -**(- ) - 2$/#
"'*'$''0($)/$*)># .#*2 #$)/# + -.*)$.0. 4/# 1  $'$)"
+-*% /*->!$)/1$-/0'.#*2*!/# 1$-/0'*4*!/# + -.*)) . )
$- / /*2-./# 2''>($--*-- !' /$*)*!/# 1/-- +- . )/$)"/# + -.*)
)'.* . )>
  0.  /#-  $!! - )/ - ) -$)" ( /#*.= #  !$-./ 2. .$(+'  + ) . 
$)/ -+*'/ .#$)">#$.2. 0. !*-/#  3+ -$( )/'. '$) <)2  - ! -/*
/#$. . . '$) > # . *) 2. /# .(  . /#  !$-./<0/ '.*$)'0  4)($
.#*2.) - !' /$*). H$"0-  UI>  - ! -/*/#$. .  - ) -$)"># /#$-
/4+  *! - ) -$)" 2. !0'' "'*' $''0($)/$*) 0.$)" /#  1$-/0' '$"#/ !$ ' HI
( /#*  .-$  $) /#  ) 3/ . /$*) H$"0-  U<I> #  4)($ .#*2. )
- !' /$*).2 - $ )/$'$)/# )*)$/$*).>$"0- V.#*2.+ -.*)$)
/# 1 2$/#/# . ) - ) - 0.$)"/# ( /#*>
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
\
# +-/$$+)/2.- +- . )/ 41$-/0'#0()*$#-/ -H*-1/-I># - 
2.! (' )(' 1/-1$''  + )$)"*)/# " ) -*!/# +-/$$+)/
H$"0- UI>$) $)1 +-/$$+)/.). /# $-*2)- '*4</# 1/-2.
$)1$.$' < 3 +//#/ $/*0'./.#*2. )- !' /$*)..$!$/ 2 - 1$.$' ># 
1/- 2. ,0$/   /$'  *(+-$.$)" ++-*3$(/ '4 TS +*'4"*).< / 3/0-  )
#)?-$""  !*- - '$./$ .&$)  !*-(/$*).<  + )$)" *) /#  +*.  *!  .& ' /'
./-0/0-  (   2$/#$) /#  (* '> #  1/- (* ' 2. !-*(   .$")
H222>345 .$")>*(I>/2.)$(/ 2$/#$)1 -. &$) (/$. -$1 *)'4!-*(
# /-& -)2)< #2$/#Y "- .*!!- *(># ( /#*'.*0. 
- '/$1 +*.$/$*)) )"'   /2 ) /#  #  ) /#  2) /* ./$(/ /#  '*2
+*.$/$*)>#$./# - !*- +-/$''4 - +'$/ /# +-/$$+)/B.- '*4(*1 ( )/.<
/# $--$"#/ #) #*'$)" /#  2)- .0'/ $) /#  1/-B. -$"#/#) -( (*1$)"
*-$)"'4< . 2*0'  . )$) /#  ($--*- - !' /$*)) .#*2. *!/#  1/->
*- *1 -< # ?/0-). 2 -  '.* *-- /'4 - ) -  *) /#  1/- - +- . )//$*)<
)0+)*2)*4(*1 . 2*0' '.*   . )/* - !' / $)/# ($--*-<.
2*0'2#*' *4/0-).>

) *- - /* +-*1$ "'*' $''0($)/$*) / - '?/$( !-(  -/ .2   1 '*+  
#4-$- ) -$)"( /#*>  (+'*4 /# $-/0'$"#/$ 'HIJWK$)*- -/*
*0)/!*-"'*'$''0($)/$*) !! /. /2 )/# .//$ ' ( )/.*!/# . ) >#$.
*0)/.!*-!0''LFFMN$''0($)/$*)$).//$ )1$-*)( )/.<)/#0..*'*-
' $)" !! /.<0./$- !' /$*).0 /*.0-! .2$/#)*)?$!!0. .).*!/
.#*2.> #   .. )/$''4 ./*- .  .(+'$)" *! /#  *0/"*$)" -$)  !-*( ''
+*$)/. $) /#  . )  $) '' $- /$*). ) /#$./ )   $)/ -+*'/  /* +-*0 
- ) -$)".!-*(-$/--41)/" +*$)/.># !*-. ) ) *(+0/ *)
 $) '$) - /$(  $)/#  )0( - *! +*'4"*). ) +-*1$  .*'0/$*). 2$/# / ). *!
/#*0.).*!+*'4"*). 2$/#($''$*).*!H$-I-$)  ' ( )/.$) ($)0/ .> *0'
/# ) 0.  /#  *)1 -"   !*- - '?/$(  - ) -$)" $)" *)'4  .('' *)./)/
/$( *.//*/-$/$*)'- ) - ->
)/ "-/$)" 4)($ #)" . $)/*  "'*' $''0($)/$*) .*'0/$*) $.  $!!$0'/ /.&>
*2 1 -< 4 - &$)"0+ /#  +-*' ( ) //&$)" /#  (* . *! '$"#/ /-).+*-/
/#/ *)/-$0/  (*./ /* /#  $("  2  ) #$ 1  - '?/$(  ) ./$'' .0++*-/
.$")$!$)/"'*'$''0($)/$*) !! /.> ). +-/ /# +-*' ($)/*/#- ($)
(* .*!/-).+*-/*)/-$0/$)"/*/#  $("  ) !*0.*).*'1$)" /# . =HTI$ '
-$)  .// -  *!! /#  1/- /*2-. /#  4  HUI .*!/ .#*2. ./ 4 /# 
1/-<)HVI.+ 0'-- !' /$*).*!/# 1/->#$.* .)*/.*'1 !*-- !' /$*).
!-*(/# 1/-<)/#0.*'*-' $)"0. 4/# 1/-2$'')*/ *0)/ 
!*-> *2 1 -< /#  (")$/0  *! $''0($)/$*) /#/ #. 0) -"*)  (0'/$+'  $!!0. 
- !' /$*).$." ) -''4'*2).'$//' /*/# $(" >
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TS
) *- - /* .*'1  HTI 2  )  /*   '  /* -+$'4 +-*1$  /# $--$) /)
-$/--4.+/$'+*.$/$*))$- /$*)> ) *- -/*+-*1$ $--$) '0'/$*).
/- '?/$( !-( -/ .2 0. )$--$) 1*'0( JX<YK># *0)$)"1*'0( *!
/# . ) $..0$1$ $)/*. /*!1*3 '.>1*3 './*- .$--$) - /-$ 1 !-*(
/#   +-*% /  /*  .+# -$' #-(*)$ HI> --$)  1'0 . / -$/--4
+*.$/$*).) $)/ -+*'/ !-*() $"#*-$)"1*3 '.>
#4.$''4 *-- / .*!/ .#*2. -  )*/*-$*0.'4 $!!$0'/ /* '0'/ > *2 1 -<
+ - +/0''4*-- /.*!/.#*2. )   - ) -  $) - '?/$(  0.$)"/# "-+#$.
+-* ..$)" 0)$/ HI>   0.  /#   - )/ '*. - *!/ #*2. ( /#* JZK /*
.(+'   ./)- .#*2(+ ./*#./$''4 /*+-*1$  ++-*3$(/  0(-)
+ )0(-- "$*).*!.#*20 /*)- '$"#/.*0- >
 !' /$*).H)0./$.I- '- 4++-*+-$/ '4*0)/ !*-$)/# !*-/# 
.//$+-/.*!/# . ) <0//#$.*1$*0.'4 * .)*/$)'0  /# 4)($ ' ( )/.>
#$. ) .$'4   #$ 1  $) - '?/$(  0.$)"  - !' /$*) - ) -$)" +.. J[K<
- ) -$)"/#  1$.$'  . )  ) 4)($ *% /. *)/* - !' /$1 .0-!  2#$# $.
/ 3/0- (++ /*/# .+ 0'-" *( /-4>
#  !! / *! /# .  / #)$,0 . 0.  $) *)%0)/$*) $. ,0$/  ./-$&$)"> #  4)($
' ( )/.( -" 2 ''2$/#/# .0--*0)$)". ) ! /0-$)"$(+$)"$)"*'*-' $)"<
0./$.)./$)".*!/.#*2..2 ''. $)"1$.$' $)- 8 /$1  .0-! .
H$"0- .U)VI>

#  3+ -$( )/ 2.  2$/#$)?"-*0+.  .$") 2$/# /2* "-*0+.> */# "-*0+.
3+ -$ )  !$-./ /#  . '$)  *)$/$*)> )  "-*0+ 3+ -$ )  ) 3/ /#  
*)$/$*)).0. ,0 )/'4/# ># */# -"-*0+ 3+ -$ ) /# $-. *))
/#$- 3+*.0- ..!$-./)/# )>#$.$..0((-$5 $)' T>
  0.   2$/#$)?"-*0+.  .$")  0.  2   !$)$/ '4 2)/  /* *(+-  /# 
- .0'/.*! #+-/$$+)/"$)./#$(?*-# -. '!-*../# /2**)$/$*).> )'$& 
/#  3+ -$( )/  .-$  $) -/ T H2#$# '.* $.0.. . $..0 . .0--*0)$)"
 /2 )?) 2$/#$)?"-*0+  .$").I 2   '$ 1  /#/ /#  $!! - ) . /2 )/# 
) *)$/$*).2 - .0/'  )*0"#/#/ +-/$$+)/.2*0')*/*1$*0.'4
- '$5  /#  +0-+*.  *! /#  3+ -$( )/< ) /# - !*-  /# $- - .+*). . 2*0'  
0)'$& '4/* $. 4/#$. &)*2' " > ) /# */# -#)</# $- - .+*). ./*/# 
1 )/.$)/#  )1$-*)( )/ *0' #)"  $)/# $-.0. ,0 )/ 3+*.0- >*2 1 -<$!
2  *).$ - *)'4 /#  - .0'/. *! /# $- !$-./ 3+*.0-  !/ - /#  . '$)  H2#$# *!
*0-. 2. $/# -*-I/# )/#$.)'.* )'45. /2 )?"-*0+.
3+ -$( )/>
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TT
#" 
 

! 

 "  

. '$)  )/ -+*'/ 
#$)"
* *
 )/ -+*'/ 
#$)"
 .  .
 '*'
$''0($)/$*)
 .  .

2 )/4 *)  +-/$$+)/. 2 -  - -0$/  !*- /#  3+ -$( )/ HY ! (' I< 0/ /# - 
2 - ($..$)"/!*-*) 2#$# #./# - !*- #. ) 3'0 !-*('')'4.$.
+- . )/  # - > #  +-/$$+)/. 2 -  - -0$/  !-*( -*0) /#  (+0. /
)$1 -.$/4 *'' "  *)*) ) /# 4 2 -  +$ /#  ,0$1' )/ *! RTS !*- /# $-
+-/$$+/$*)> #  3+ -$( )/ 2. ++-*1  4 /#   /#$. *(($//  0) -
$)!*-(  *). )/>   #1  +- +-   1$ * *! /#  ($) +-/ *! /#  3+ -$( )/
2#$#$.1$'' *)'$) H222>4*0/0 >*(E2/#@1`UO??[I>
+*) )/ -$)" # *! /#  )1$-*)( )/. +-/$$+)/. 2 -  !$-./ $)1$/  /* '**&
-*0))- +*-/2#//# 4.2>#$.2./* . /# ($)/*/#  )1$-*)( )/)
'.*!*-0./*# &/#//#  ,0$+( )/2.+-*+ -'42*-&$)"># - 2..*!/(0.$
+'4$)"$)/# &"-*0)>
# 4!$-./ 3+ -$ ) /# . '$) *)$/$*)<$)*- -!*-/# (/* *( +/ 
/*/#  )1$-*)( )/>#$.. '$) *)$/$*).$(+'4 .#*2  /#  1$-/0''$--4< 0/
)*//# 1/-- !' /$*).)*-)4 4)($ .#*2.< ) )* 1 )/. *0-- > # 
. '$) './ !*-TXS.<2# - /# +-/$$+)/..$(+'4'**& /)(*1 -*0)
/# -**(>
 3//# 4 $/# - 3+ -$ ) /# *)$/$*)*-/# *)$/$*)*-$)"/*
+- ? / -($)  -)*( *- -> # $- /#$- 3+ -$ )  2. $) /#  - ($)$)"
*)$/$*)> ) */#/# $- . *) )/#$- /-$'. /#  3+ -$ )  2./#  .( < )
# './  !*- T[S.># 4 .2  - !' /$*)$) /#  ($--*-*! ) 1/-2$/# 0++ -
*4(*1 ( )/./#/ +-/$''4!*''*2 /# $-*2)(*1 ( )/.. .-$ *1 >
#  /.& "$1 ) /* /# +-/$$+)/.2. /* 3($)  /# **&/$/' .> # 4 2 - /*'
/#/ $) /#  **& /$/' . /# -  2.  '0  . /* 2#/ 2. #++ )$)" 2$/#$) /# 
)1$-*)( )/> #$. 2. *)'4 /* )*0-"  /# ( /* (*1  ) '**& -*0) /# 
)1$-*)( )/<)#)**/# - 3+ -$( )/'+0-+*. >
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TU
!/ - T ($)0/  $)/* /#  . *) ) /#$- /-$'. **&. ./-/  /* !'' !-*( /# 
**&.# '1 .<*)/-*'' 4+#4.$..$(0'/$*)>//#  ) *! /# + -$**! !''$)"
**&.<*) 2. ' !/$.+'4 *)/#  # *!/# ($--*- 1/- - !' /$*)> 2 - 
0-$*0./*. #*2/# 42*0'- //*/#$.<.$) )// (+//*/*0#/# $-# /*
! ' /#  1$-/0' **& . ) *) /#  ($--*-  1/- #  2*0'  .$") *! . '!?
- *")$/$*)'' /# $--*-  ./> *2 1 -</#$.2.)*/ *)  *! /#  3+ -$( )/'
$..0 .> ) */# . *) ) /#$- 3+*.0- . !/ -  !0-/# - T ($)0/   1$-/0'
#-/ -++ - $)/# -**(>#$.#-/ -2.*42#*!'*/ -*0)/# 
-**(/#-  /$( . ) /# ) $.++ - >-/$$+)/.2*0'/4+$''4 !$-./ . /#$.
#-/ - $) /#  ($--*-> #  +0-+*.  *! /#$. 1 )/ 2. /* $)% /  .#*& $)/* /# 
)1$-*)( )/<0. !0'!*- ( .0-$)" $!! - ) . $) +#4.$*'*"$' - .+*). . /2 )
/# *)$/$*).>
/ /#  ) *! # *! /# $- /#-  3+ -$ ) . /#  . )  2. - +'  4 / 3/
*)/$)$)"/# ,0 ./$*))$-  .-$ $)/# ) 3/. /$*)>!/ -).2 -$)"''*!/# 
,0 ./$*)./# +-/$$+)/.2 - $)./-0/ /*'*. /# $- 4 . 0)/$'/# ) 3/. ..$*)
./-/ >
1 -''/#  )1$-*)( )/#.*( 2#/./-)" .+ /< 2$/# **&/$/' .+*$)/$)"
/*2-.+-)*-(' 1 )/.>'.*/# **&.!''$)")/# .0 )++ -) *!/# 
!'*/$)"*4 /*/#$.<.$/# &"-*0)(0.$>

//#  )*! #. ..$*))2#$' /# +-/$$+)/.2 - ./$''$)/# 1 . -$ .*!
,0 ./$*).2.$.+'4  *) /# 1 2''.<) /# 42 - .& /*.*-  # *) 
*)S/*TSS.' 2# - TSS2./# (*./+*.$/$1 - .+*). ># ,0 ./$*).2 - 
.!*''*2.=
T>.*( /$( .! '/(4. '!/* $)/# '$--4(0#.$!2.$)- '+' >
U># )/#$)&*0/$/)*2- ( ( -/# '$--4(*- .$! $/ 2 -   +'  
1$.$/ -/# -/#)*(+0/ -" ) -/ 2*-'>
V>  .*( /$( . !*-"*/ *0/ /#  - ' 2*-' *! /#  '*-/*-4) - /  . $! 
2 - $)/# '$--4>
W>.*( /$( ./#*0"#/*0/.$//$)"*)/# #$->
X>.*( /$( ./#*0"#//#//# +')/($"#/ - '*) >
Y>*( /$( .(4/#*0"#/.<! '$)".)/$*).2 - .$!2 - $)- '+' >
Z>1 ) /#*0"#/# + -.*)$)/# ($--*-$)*/'**&'$& ( .*( /$( .#/# 
! '$)".$!2 - . $)"(4. '!>
0 ./$*). T< U< V ) Y - '/  /* +- . ) > W ) X 2 - /* 3($) 
2# /# - /#  "- / - $''0($)/$*) - '$.( 2*0' #1  ) $(+/ *) /#   "-  *!
- '$.(*!/# $)$1$0'*% /.># )+-/$$+)/.2 - .& /*"$1 /# $-.*- .
0-$)" /# $- . *) ) /#$- 3+*.0-  /# 4 2 -  '24. - ($)  *! /# $-
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TV
+- 1$*0. .*-  !*- /#  .(  ,0 ./$*)> Z 2. !*- 0-$*.$/4 /* 3($)  *1 -''
2# /# - . $)" /# ($--*- - !' /$*) 2*0' " ) -/   ! '$)" *! *4 *2) -.#$+
2$/#- .+ //*/# 1$-/0'*4<)$..0 /#/2.)*/*) -)*!/#$. 3+ -$( )/>
 
#  +-/$$+)/. 2 -  !$//  2$/#   30. W +#4.$*'*"$' - *-$)"  1$  /#/
- *- /# >' /-* .2 - +' *)/# ' !/)-$"#/*''-*) .)/# 
'*2 ./' !/-$$)*- -/*- *->
#   $) /#$. 3+ -$( )/ 2. ,0$-  . ./)- $)/#*1 )   -$1/$*)
H.(+'$)" !- ,0 )4= TSUW 5I ) /#  )'4.$. 2. + -!*-(  2$/# /# 
">)'45  $*.$")' )'4.$..*!/2-  +&"  H">/  G 0" -  #)*'*"$ . <
-5< 0./-$I> .$)" /#$. .*!/2-  /#   H1 )/-$0'- *)/-/$*)I *(+' 3 .
2 -  / -($) <)$).+ / )()0''4*-- / 2# - )  ..-4># 
*(+' 3 .- /# /$( $./) .!-*(*) # -/*)/-/$*)/*/# ) 3/*) >)A
$)/ -1'B( )./#/*)'4)*-('?/*?)*-(' /$./) .- - /$) H)*)?)*-('
 /..0#. 3/-.4./*' .-  3'0 I># ( .0- .- /$) 2 - =
G/# ( )# -/-/ *1 -/# U($)0/ + -$*H+(I>
XS?)0( -*!$)/ -1'.*!.0 ..$1 $)/ -1'."- / -/#)XS(.>
# .  ( .0-  -  3+'$)  $) ). /. $) JTK> )3$ /4 $. " ) -''4 3#$$/  4
#$"# -# -/-/ )'*2 -# -/-/ 1-$$'$/4<# - ( .0- 4XS>
$/$*)''4 2  *(+0/  # -/ -/    ' -/$*) HI 2$/# - .+ / /* Y.
$)/ -1'. !/ - /#  .+ $!$ 1 )/ *! /#  *4 ++ -$)" $) /#  ($--*->  $. /# 
) "/$1 *!/# .'*+ *!$)./)/) *0.( .0- !-*(%0./ !*- /# *). /*!/# 
1 )//*/# ($)$(0( //$)  $) /#  Y. !/ - /#  1 )/> / #. ).#*2)/*
*-- '/ 2$/#./-*)") "/$1 ! '$)".J\KH+X[[I>


$"0- W.#*2.-#-/.!*-/# ,0 ./$*))$- - .+*). .T?YH)`T\<.$) *)
.0% /2.- (*1 2#*"1 S.*- .*) 1 -4,0 ./$*)I>/.#*0' )*/ /#/
/#  .*- . !*- /#  +- . )  - '/  ,0 ./$*). T?V ) Y -  - '/$1 '4 #$"#
*1 -''>/$.' -/#//# - $.)**- - !! /.$) /# - #-/. .#*2 /#  .( 
+// -)*!- .+*). .2$/#$)*/#)>)# ) /# 2$/#$)?"-*0+. .$")$.
++-*+-$/ > / $. '.* ' -/#/ !*- /#  ,0 ./$*). /#/- '/  $- /'4 /* +- . ) 
HT?V) YI /# -  ++ -. /*   ) $)- . $).*- !-*(/#  . '$)  /* /# 
3+ -$( )/' *)$/$*).< 0/ /# -  $. )* $!! - )   /2 ) /#  3+ -$( )/'
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TW
*)$/$*).> #  $  *! .$//$)" *) /#  #$- HWI / )  /* *0- /* + *+'  (*- 
0-$)"/# . '$) 0/ )*/.*(0#$)/#  .0. ,0 )//-$'.>'.*/# $''0.$*)/#/
/# +')/($"#/ - 'HXI/ ) /**0-(*- $)/# *)$/$*)/#)$)/# 
. '$)  *-  *)$/$*).> *2 1 -< /#  *)'4 ./-$/'4 1'$ *(+-$.*). - 
 /2 )/# ) *)$/$*).< .$) /# *)'4$!! - )  /2 )/# . 2.
/# *1 -'',0'$/4*!/# $''0($)/$*)H$)/# . '$) /# -  2 - )* 1 )/.<))*
1/-- !' /$*)I>
$) /# - - )**- - !! /.2 )--4*0/+$- / ./.*)/# *($) /
$")*-$)" *- - $) *- - /* *(+-  - .+*). . /*  )  H$> >< #
+-/$$+)/B. .*- . $) *)  *)$/$*) $. *(+-  2$/# #$.? *- # - .*- . $) /# 
*/# -I>   0.  /#  )*)?+-( /-$ .$") / ./ /#-*0"#*0/ .$)  $) /#  .  *! /# 
,0 ./$*))$-  - .+*). . ) ` T\ ) /#  / $. *-$)'> *- /# ,0 ./$*))$- 
- .+*). ./# -  - )*.$")$!$)/$!! - ) .*))4*!/# ,0 ./$*). /2 )
)># .('' ./.$")$!$) ' 1 '.- `S>TT!*-X)'.*!*-Y>
OV VO
0
20
40
60
80
100
Q1
OV VO
0
20
40
60
80
100
Q2
OV VO
0
20
40
60
80
100
Q3
OV VO
0
20
40
60
80
100
Q4
OV VO
0
20
40
60
80
100
Q5
OV VO
0
20
40
60
80
100
Q6
Baseline
OGL
VLF
$"0- W?-#-/.!*-/#  .+*). -$' . ?#*2$)"/#  ))/)-
--*-.!*-T?Y>$./# "-*0+/#/ 3+ -$ ) /# *)$/$*)!$-./<)$.
/# "-*0+/#/ 3+ -$ ) /# *)$/$*)!$-./>
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TX

 /**& /#  ($'  U ($)0/ . !-*(/# - *- .$")'.*! # . ..$*))
*(+0/ /# )XS1'0 .># *1 -''( )H±I.H /.+ -($)0/ <
+(>I- '(*.//# .(  /2 )/#  3+ -$( )/'*)$/$*).=\T>[±TY>\+(
HI)\T>W±TZ>S+(HI> $($'-'4 /#  ( ) XS*0)/.- '(*.//# 
.( =TS>V±TW>THI)[>[±TU>XHI>#0.*1 -''/# - $.)*$)$/$*)*!
#$"# -./- ..$)*) *)$/$*)*(+- /*)*/# ->
*2 1 -< /# -  $. *)  1 -4 $)/ - ./$)" - .0'/ - '/  2$/# >   /&  
*). -1/$1  ( .0-  *! /#  *1 -'' ' 1 ' *! +- . )  4 *(+0/$)" !*- #
$)$1$0'/# )0( - *! /$( . /#/ #  *- .#  "1 .*- *!/ ' ./ ZS] *) /# 
,0 ./$*). T?V ) Y> #$. /-).!*-(. /#  +- . )  .*- . $)/*  *0)/< )
*-- .+*). /* 2#/ 2  #1 0.  $) -'$ - ++ -. ? >"> JTSK>  /B. '' /#$. /# 
A+- . )  *0)/B ) +'*/ /#$. *) /#  #*-$5*)/' 3$. "$)./ # -/ -/  *) /# 
1 -/$' 3$.< .#*2) $) $"0-  X> # -  $.  ' - '$) - +*.$/$1  /- )< ) /# 
*-- '/$*) $. #$"# H- ` S>XT<  a S>SST< ) ` V[I /&$)" *0)/ *! ($..$)"
*. -1/$*).>H# -  -  US .0% /. # *! 2#*$/# )  *)$/$*).
)/#0.WS/+*$)/.>U- '*./<T #$))< 0. *) +-/$$+)/
).2 - S$)'',0 ./$*).I>
        









!"$##$! $"#"$#%#"!"#"#
!##
$"0- X?+(4+- . ) *0)/>
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TY
&"'
*0.$)" $) (*-  2  ) 3($)  /#  $(+/ *! /#  +-/$0'- 1 )/  .$")  /*
0.   .0-+-$.  *- .#*&< 2#$# 2. 2# ) /#  1$-/0' *4 !'*/  $)/* /# 
)1$-*)( )/> #$. $ +-*0  1$.$'  .#*&. $) TS *! /#  .0% /. $) /# $- !$-./
3+*.0- <).*( *!/# (/0''4.- ( 2# )/# 4!$-./.2/# *4>)*- -
/* 3($) /#$.+#4.$*'*"$''4<2 *(+0/ # -/-/   ' -/$*)HI!*-/# 
Y.+ -$*!/ -/# *4 )/ - /#  )1$-*)( )/> #  ./ + - /#  ' -/$*)/# 
"- / - $)$/$*) *! ) "/$1  1' ) >   *(+-  /#$. 2$/# /#  Y. + -$* /#/
./-/ TS. !*- /# *4 )/ - /#  )1$-*)( )/.*)/-*'>*-/#$.1-$' 
2  3+ /  ) *- -$)" !! /< .$)  /#  . *) /$(  /#  !0'' . )-$* 2.
$.+'4 </# - *0' "**"0 ..*0/2#/2*0'*0->
' U
 ).)/)- 1$/$*).*!/#  -//   ' -/$*).!*-TS. !*- /# 
*4)/ - )./-/$)"!-*(/#  1 )/$/. '!>
# 1'0 .- !-*(/# .$")/ ./H)`TS$) # ''I>
 
-$' TS.
 !*- 
1 )/  TS.
 !*- 
1 )/ 
U X>W±X>Y \>V±US>X T T>\±W>V TT>Y±TY>W S>SSU
V Y>Y±TS>T W>V±[>T T Y>Z±TS>[ X>\±TT>S T
#   1'0 . -  '0'/  . /#  ) "/$1  *! /#  .'*+ < .* "- / - 1'0 .
$)$/  "- / -   ' -/$*)> -*( '  U 2  ) .  /#/ /# -  $.  .$")$!$)/
$!! - )  /2 ) /#   TS.  !*- /#  1 )/*! /#  *4 )/ -$)"<) !*- /# 
1 )/$/. '!?0/*)'4!*-/#*. $)/# *)$/$*)>#$.*0-- *)'42# )/# 4
3+ -$ ) /#$. 1 )/!*- /#  !$-./ /$( < /#/ $. 0-$)" /# $-. *)/-$'H/# !$-./
!/ -/# . '$) I>)/#$.. /# ( )1'0 .- .$")$!$)/'4#$"# -!*-/# 
1 )//#)!*-/# TS. !*- /#  1 )/>*/*)'4$./#$./# . *)/# 1 -" <0/
$/ $. .* !$ ($* !  ! &10 "$&" &%> #  !/ /#/ /# -  2. )* .$")$!$)/
$!! - ) $)/# $-. *) 3+*.0- /*/#$. 1 )/H/-$'VI.#*2./#//# - # )
+//$*)>
.  !0-/# - *(+-$.*)2  --$  *0/ .$($'- )'4.$. !*- /#  1 )/ 2# ) /# 
**&. ./-/  /* !''> ) /#$. .  /# -  2 -  )* .$")$!$)/ $!! - ) . / '' H/# 
'*2 ./1'0 (*)"./ /#*.  ,0$1' )//*'  U 2.S>TTI>#$.$''0./-/ ./#/
/# 2.' /*$./$)"0$.# /2 )) 1 )//#/. 1 -'+-/$$+)/.!*0)/*
  !-$"#/ )$)" ) )*/# - 1 )/ /#/ '/#*0"# $/ 2. 0)0.0'< # )*/  )
 .$") /*#1 ) "/$1 1' ) >
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
TZ

0((-$5$)"/# $(( $/ - .0'/.2 #1 !*0)/#/=
• # - - )* $!! - ) .*))4+- . ) ,0 ./$*))$-  .*- /2 )
)  $)$/$)" /#/ /#  ' 1 ' *! +- . )  2. )*/ $)!'0 )  4 /# 
- ) -$)"/4+ >
• # -  -  )* $!! - ) . *) *1 -''  ( .0- . H# -/ -/  ) XSI
/& )*1 -/# ($' U($)0/ .*!/#  3+ -$ ) <$)$/$)"/#//# - 2.
)* *. -1'  *1 -'' +#4.$*'*"$' $!! - )  .0# . ./- ..  /2 ) /# 
*)$/$*).>
•  -/ -/  $. .$")$!$)/'4 +*.$/$1 '4 *-- '/  2$/# ) *1 -'' ( .0-  *!
+- . ) >
• *).$ -$)"/# !$-./ 3+*.0- .*)'4*! $/# -/# *-*)$/$*)</# - 
$.  ./-*)"  !! / 2$/# - .+ / /* /#  .+ $!$ 1 )/ *! 1$-/0' *4
)/ -$)"/# -**($)/# *)$/$*)0/)*/$)/# *)$/$*)>
!2  "* & ) - *).$ - /#  ( )$)" *!/#  3+ -$( )//#/ 2   .-$  $)
-/T<$/$.)*2' -/#/$/2./# 4)($#)" ./*.#*2. ) - !' /$*).
*-- .+*)$)" /* *4 (*1 ( )/. /#/ (// - < ) )*/ /#  ,0'$/4 *! /# 
$''0($)/$*)> ) 2# ) /# 4)($#)" .- /#  .( $)/2**)$/$*).0/
/# $''0($)/$*)/4+ 1-$ .<.$)/# ) 2 3+ -$( )/<2 *)*/!$)/#$.$!! - ) 
$)+- . ) >
# .  !$)$)". )   +0/ $)/* /#  *)/ 3/ *!  ) 2 ++-*# /* +- . )  /#/
$./$)"0$.# . /2 )/2*$!! - )/*(+*) )/.=' ''0.$*) HI)'0.$$'$/4
H.$I JTT< TUK H.  ). /I>  - ! -. /* /#  *-$"$)' $  *! +- . )  . /#  ./-*)"
$''0.$*) *!  $)" $) /#  +'  +- . )/  4 /#  1$-/0' - '$/4 $.+'4.> #  ) 2
++-*# .0"" ./.  /*   '-" '4  !0)/$*) *! /#  . ).*-$(*/*- *)/$)" )$ .
!!*-  4 /#  $.+'4)/-&$)" .4./ (.> #  (*- /#/ + *+'  )0.  /# $-
2#*' *$ ./*--4*0//.*!+ - +/$*)$))*-('24</# "- / -/# #) 
!*-/**0-> ) <!*- 3(+' <2$  !$ '?*!?1$ 2< ./ - *# ?/-& # 
(*0)/  $.+'4 $. (*-  '$& '4 /* '  /*  /#)  )--*2 !$ '?*!?1$ 2 0/
*/# -2$. .$($'-.4./ (<*-/#-*0"#'**&$)"-*0)/#  )1$-*)( )/4<.4<0.$)"
 %*4./$&> $/# - .+ / /* /#   )  *)$/$*). /#  !!*-) . !*-
+ - +/$*)2 - /# .( G$)/# 1 2$/## /-&$)"?)/# - !*- 2 2*0'
)*/ 3+ //*!$)$!! - ) .$)- +*-/   .  /2 ) /# .  /2* *)$/$*).< )
/#$.$./# . >
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
T[
). /*)' ''0.$*))'0.$$'$/4
#  *) +/ *! +- . )  #. -  )/'4  )  *)./-0/  $)/* /2* *-/#*"*)'
*(+*) )/.JTT<TUK=# !$-./$./# +0- $''0.$*)/#/+-/$$+)/.#1 /#//# 4
- '*/ $)/# +'  +$/ 4/# 1$-/0' )1$-*)( )/? /#$.$.A' ''0.$*)B
HI># . *)$./# $''0.$*)/#//#  1 )/./#/- ++- )/'4#++ )$)"$)/#/
+' - - ''4#++ )$)">   ''/#$.'0$'$/4''0.$*)H.$I># .  $''0.$*).
- +-*0 4*0-+ - +/0')*")$/$1 .4./ (.<)*0-$).+$/ *!*0-#$"#
' 1 '&)*2' " /#/2 - <!*- 3(+' <A- ''4B$)'*-/*-42 -$)" ,0$+( )/
/#/" ) -/ . /# . ).*-4/?./- (/#/' . /*/# . $''0.$*).># . $''0.$*).
- 0/*(/$< 4*)*).$*0.*)/-*'>
# +#4.$'.$.*!$./#*0"#//* % %!$!&!$! &  %/#/*-- .+*)
/* /#*.  *! +#4.$'- '$/4> ).*-$(*/*- *)/$)" )$ . -  /#  $(+'$$/ -0' . /#/
2 &)*2*) -)$)"#*2/*0. *0-*4/*+ - $1 /# 2*-'>*- 3(+' < 2 
&)*2/#/ /* .   #$) ) *% /2 #1 /* (*1  *0- #  /* /# .$  /* -$)"
+-/.*!/# . ) /#/- *.0- $)/*1$ 2># ).*( *) + - $1 .4--4$)"
*0/ /$*). /#/ - .0'/ $) #)" . $) H(0'/$. ).*-4I $(" . 4 0.$)" /# $- *4
(0# . $) +#4.$' - '$/4</# )/#  .$(+' ./ #4+*/# .$. !*-/#  -$) /* *+/$.
/#/ 2#/ $.  $)"+ - $1 $. /0''4 /# -  ?$> >< /#/ /# + -.*) $. $) /#  +' 
 +$/ 4/# 1$-/0' )1$-*)( )/>
# +#4.$'.$.*! .$ $./#*0"#//* /#  3/ )/ /*2#$# HI /# ++'$/$*)$.
+-*"-(( /*+-*0  1 )/./#/*-- '/ 2$/#/#   #1$*-*! /# +-/$$+)/<
HI #*2 (0# 1 )/. $) /#   - ! - + -.*)''4 /* /#  +-/$$+)/< ) HI /# 
1'$$/4 *! /#  . )-$* 2$/# - ! - )  /* .$($'- - ''$!  .$/0/$*) $)2#$# /# 
1 )/. +$/ ($"#/*0->
#4- /# . $''0.$*).)  ..-4!*-.0 ..!0'++'$/$*).@("$) 4*0 )/ -
$)/*1$-/0'- '$/4!*-/# -+ 0/$+0-+*. .?!*- 3(+' <!*-*1 -*($)"+#*$
*!.+ &$)"$)+0'$>#   +0/. 4*0 $)/# .$/0/$*)*! $)"$). ($)--**(
./)$)" $) !-*)/ *! ) 0$ )  JK> ! 4*0 * )*/ #1  /#  $''0.$*) /#/4*0 - 
/# - <$)/#/+' <)*)3$ /42*0' " ) -/ >$($'-'4$!4*0*)*/#1 /# 
$''0.$*)/#//# - - + *+' /# - 2#*- - .+*)$)"/*4*0- #1$*-<"$)$/$.
0)'$& '4/#/)3$ /42*0' " ) -/ > /0)' ...*(  "- *!)3$ /4*0-.
/#/$.*)*($/)/2$/# 2#/ 4*02*0' 3+ -$ ) $)*-- .+*)$)"- '+' 
).$/0/$*)</# )$/2*0' )*/   +*..$'  /* 0.  /#$. ++'$/$*)!*-/# -+ 0/$
- .*).>*( 0/*(/$''4- .+*)$)"+-/*!/# -$)(0./#1 /# $''0.$*)/#/
4*0 -  ./)$)" $)  -**( 2$/# ) 0$ )  '**&$)" / 4*0< ) " ) -/  /# 
+#4.$*'*"$' ) (*/$*)' - .+*). . /#/ "* '*)" 2$/# /#$.> #  !/ /#/ 4*0
- ''4&)*2/#/4*0- )*/$)/#/+' $.$-- ' 1)//*/# .0 .. *! /# 
++'$/$*)>
*/& )*/# - 3(+' <.*$'+.4#*'*"$./$.--4$)"*0/) 3+ -$( )/*)#*2
+ *+' - .+*)/*1$*' )/$)$ )/.<.0#.!$"#/ /2 )/2*+ *+' $)-JK>
0# 3+ -$( )/.))*/  --$ *0/$) +#4.$'- '$/4!*- /#$')+-/$'
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
T\
- .*).>*2 1 -</# 4) --$ *0/$)1$-/0'- '$/4>*-.0# 3+ -$( )/./*
 1'$/#  3+ -$( )/'1*'0)/ -.(0./#1 /# $''0.$*)/#//# 4- $)/# -
2# - /# !$"#/$.*0--$)"HI)/#//# !$"#/$.- ''4#++ )$)"H.$I>$/#*0/
/#*.  ./-*)" $''0.$*). /#  3+ -$( )/' ./0$ . 2*0' )*/   0. !0'< .$)  /# 
++-*+-$/  +#4.$*'*"$'< (*/$*)' )  #1$*-' - .+*). . 2*0' )*/  
!*-/#*($)"> "$)< 2  -  .+ &$)"*!0/*(/$ - .+*). . /#/*0-$).+$/  *!
4*0-#$"#' 1 '*")$/$1  &)*2' " /#/$)!/4*0 -  - ''4 $) .4./ (<)
/#/)*/#$)"/#/$.++- )/'4#++ )$)"$./0''4#++ )$)">
JK > >  -/0< > '/ -< ) > -& -< C) 3+ -$( )/ *) +0'$ .+ &$)"
)3$ /4 $) - .+*).  /* /#-  $!! - )/ /4+ . *! 1$-/0' 0$ ) <D - . ) ?
 ' *+ -/*-.)$-/0')1$-*)( )/.<1*'>TT<)*>T<++>Y[?Z[<USSU>
JK> *1$-<>2++<>+)')" /'><C# 0. *!1$-/0'- '$/4$)/# ./04*!
+ *+' P.- .+*). ./*1$*' )/$)$ )/.<D -*)/$ -. $)  #1$*-'  0-*.$ ) < 1*'>
V=X\>*$=TS>VV[\E) 0-*>S[>SX\>USS\<USS\? ?UV<USS\>
*).$ - '.* /#  ./-*)" *-- '/$*)  /2 ) # -/-/  ) /#  *1 -''+- . ) 
*0)/ $) /#   )  3+ -$( )/' *)$/$*).> $)  /#  *1 -'' ( ) .
 /2 )/# /2**)$/$*).- .//$./$''4 /# .( <) .$)  /# - $.)*#)" 
$) # -/ -/  1-$$'$/4 . ( .0-  4 XS /#$. *-- '/$*) - .0'/ +-*'4
- !' /. /#  (*0)/ *! "*%&(&* *! +-/$$+)/. ? /#  "- / - /#  - +*-/ 
+- . )  /#  "- / - /#  (*0)/ *! /$1$/4> '.* /&  $)/* *).$ -/$*) /#  !/
/#//#$.- '/$*).#$+  /2 ) +- . )  )  )   . ) 1 )!*-/# . '$) 
*).$ - 4$/. '!?'/#*0"#)*/.*./-*)"'4H-`S>WU<`S>SZI>*/# *-- '/$*)
$. )*/ 0.  4 /#  )  ..$/4 *! +-/$$+)/. - .+*)$)" /* 1 )/.$) /#  1$-/0'
)1$-*)( )/<.$) /# - - )*) $)/# . '$) > # - !*-  $/(0./ 0. 4
.*( $)/-$).$- .+*). 4+-/$$+)/.>#$.!$)$)"* ..0++*-//# $ /#/$.
..*$/  2$/# )/0-' . ).*-$(*/*- *)/$)" )$ .< .$)  /#  *)'4 - .*) !*-
"- / - *4 /$1$/4 $. !*- + - +/$*) ? 0.$)" /#  *4 )/0-''4 !*- + - +/$*)
H >"><'**&$)")(*1$)"-*0)I>
). /*)).$
)/#  3+ -$( )/ .-$ $)JTUK/# - 2 - /2*"-*0+.*!+-/$$+)/.<*) /#/
# )$)./-0/ /**) )/-/ *)'4/# $-. )./$*)*! $)"$)/# 1$-/0'+' 
HI)/# */# -*)'4*)/# $-. )./$*)*!/# - '$/4*!2#/2.#++ )$)"H.$I>
# 4 *0' // (+/ /* *+/$($5   *- .$ 4 ./ +?4?./ + $(+-*1 ( )/. $) /# 
,0'$/4 *!  )0( - *! +-*+ -/$ . *! /#  1$-/0' - '$/4 .4./ (?,0'$/4*!
$''0($)/$*)- ) -$)"<!$ '*!1$ 2< /4+  *! $.+'4<). '!?- +- . )//$*) 4)
1/->-/$$+)/.2#*# )$)./-0/ /*(3$($5 .$ / ) /**+/(*- 
*!/ ) ) -'$ -/* $(+-*1  /#  ,0'$/4*! $''0($)/$*) /#)/#*.  2#*#  )
$)./-0/ /**+/$($5 >
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
US
.$$./# $''0.$*)/#/2#/$.#++ )$)"$.- '>#  3+ -$( )/- +*-/  $)-/T
*!/#$. ++ - ) )*2   $)/ -+- /  . .#*2$)"/#/$/2.*-- '/$*).  /2 )
*4 (*1 ( )/. ) *-- .+*)$)" #)" .$).#*2. ) - !' /$*)./#/2.
/# 0. *!/# "- / -+- . ) >#$.$.$)'$) 2$/#/# !/*-./#*0"#//*$)!'0 ) 
.$.$.0.. $)/# ). /?/# *-- '/$*) /2 )+-/$$+)//$*).) 1 )/.
$)/# >$/$*)''42 #1 !*0)/#/2.!! / $)/# *)$/$*)4
/# .0 )++ -) *!/# "#*./?'$& *4<0/ /#//#$.$ )*/ *0-$)/# 
*)$/$*)>!+-/$$+)/.2 - / )$)"/*/- //# .$/0/$*).- '/# )/# .0 )
++ -)  *! /#  *4 2*0' $)  #1   )  !-$"#/ )$)" *0-- )  )
/# - !*-  '$& '4/*$)0    - .+*). > $!$)$)JTUK/#//# - 2.
"- / - +-*$'$/4 *!  '0.$$'$/4 $''0.$*) 0) - /#  *)$/$*) *! !0'' "'*'
$''0($)/$*)2$/#4)($#)" .*(+-  2$/# -$*.$/4?'$&  .*'0/$*)H"'*'
$''0($)/$*) 2$/# )* 4)($ #)" .I> 0- - .0'/. !-*( /#$. ) 2 3+ -$( )/
.0++*-//#$.!$)$)">
$)''4<2 - +*-/ /#/Y*0/*!/# US+-/$$+)/. $/*0#/# $-*2)# .!/ -
/# 4.2/#  **&*)/# /*+ *!/# ($--*-1/- # ># ( ).*- !*- Z*)
! '$)"/#//# 1/-$)/# ($--*-2./# . '!2.X[±UZH>>I2$/#)*$!! - ) 
 /2 )/# )*)$/$*).>
("
# /& ?#*( ( .." *!/#$. 3+ -$( )/$./#//# ' ''0.$*)*(+*) )/*!
+- . )  $. )*/  !0)/$*) *! /#  ,0'$/4 *! $''0($)/$*) - ) -$)"> '  ''0.$*)
 + ).*)/# !*-(/#-*0"# 2#$#/#  )1$-*)( )/) + - $1 ?2#$#$. 
!0)/$*) *! /#   "-  *! #  ) *4 /-&$)"< ) $.+'4 !/*-. /#/ 2*0'
.0++*-/ )/0-' + - +/$*) H!$ '?*!?1$ 2< - .*'0/$*)< '/ )4< !-( ?-/ < ) .*
*)I># !!*-) *!H1$.0'I. ).*-$(*/*-*)/$)" )$ ./#/- '*. /*)/0-'<
./4+$''4*0-.$)1 .4./ (2$/## ?/-&$)"$. )*0"#/*" ) -/ #$"#
' 1 '*!' ''0.$*)>
*2 1 -< $! $) *0- ++'$/$*) 2  $( / + *+'  - .+*)$)" /* /#  1$-/0'
)1$-*)( )/ - '$./$''4< 2  '.* #1  /* /&  $)/* *0)/ /#  '0.$$'$/4
*(+*) )/ *! +- . ) > 0- - .0'/. .0"" ./ /2* /#$)".> $-./< 2# -  ++-*+-$/ 
/# -  .#*0'   1 )/. /#/ *0- $) /#  1$-/0' - '$/4 /#/ *-- '/  2$/# /# 
/$*).*!/# +-/$$+)/.>)/# . *!*0-/2* 3+ -$( )/./# .  1 )/.2 - /# 
4)($''4#)"$)".#*2.)- !' /$*).$)- .+*). /**4(*1 ( )/.>0/
*/# - .0# *-- '/  1 )/. -  '.* $(+*-/)/ ? .0# . 1$-/0' #-/ -.
- .+*)$)"++-*+-$/ '4/*/# /$*). *! /#  +-/$$+)/H)*/ *).$ -  /''$)
/#$.++ -I> *)<*0. "'*'$''0($)/$*)?$/++- )/'4* .# '+/*!*./ -/# 
$''0.$*)/#//# .$/0/$*) +$/ $.- ''4#++ )$)">
*!/ - '' 2  2*0'- *(( )/#/- '?/$(  "'*' $''0($)/$*)2$/#4)($
#)" ./*- !' /$*).).#*2..2*-/#/#  !!*-/>
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
UT
 
#$. - . -# 2. --$  *0/0) - /#    -*% / A- . )  $)  $-/0'
$"#/$ 'BHEXTT[UWETI> ''/ -B.*)/-$0/$*)2.'.*.0++*-/ /#-*0"#
/#  0-*+ )  . -# *0)$' -*% /  *)/-/ 0( - UUZ\[X>  
/#)&1$2++!*-#$.$)1'0' # '+2$/#/# 1 .4./ (>

JTK > '/ -< > #))< >*-/ ). ) & ,< C$.0'  '$.( )#) .  '$./$
 .+*).  $) ) (( -.$1  $-/0' )1$-*)( )/<D  !"'&$ $"%
 ""&! %+1*'>U\<)*>V<++>ZY?[W<USS\>
JUK >>)# 5?$1 .<)>'/ -<C-*(- . ) /**).$*0.) ../#-*0"#
$-/0' '$/4<D&'$()%'$!% +1*'>Y<)*>W<++>VVU?VV\<USSX>
JVK >$((*).<)>)/ -<C# )!'0 ) *! ) -$)" 0'$/4*)- . ) 
) .&  -!*-()  $)  $-/0' )1$-*)( )/<D  $&' &*+,
$! %,<++>U\V?U\W<USSV>
JWK > *-/ ). )< > 0< > #)) & ,< C '?$(  '*' ''0($)/$*) !*-
$-/0'  '$/4 ++'$/$*).<D !"'&$ $"%  ""&! %+1*'>
U[<)*>Y<++>XY?YW<USS[>
JXK >((**-/#$<)>)-#)<C) !!$$ )/- +- . )//$*)!*-$--$) 
)1$-*)( )/(+.<D$)USST-* $)".*!/# U[/#))0'
*)! - )  *) *(+0/ - -+#$. ) )/ -/$1   #)$,0 .< USST< ++>
W\ZGXSS>
JYK >- " -<>#$-' 4<>>0- & ,< C#  $--$)  1*'0( <D 
!"'&$$"% ""&! %+1*'>T[<)*>U<++>VU?WV<-?+-<T\\[>
JZK >-'.&4< C!!$$ )/.*!/? " .#*2.0.$)"+$3 '.# --)#$)"<D
%+1*'>U<++>UY\?U[U<USSX>
J[K > > $'"-< C(+-*1$)" .#*2. ) - !' /$*). 1$ /#  ./ )$' 0!! -<D
&"$<USSS>
J\K > $*++*< > ..$)-4< ) >  -)/.*)<  !! ! %*!"*%!!*=
(-$" )$1 -.$/4- ..<USSZ>
JTSK >'/ -<)>/ <C1$-/0' +- . )  *0)/ -<D $% -!"$&!$%
 $&' ($!  &%+1*'>\<)*>X<++>WTV?WVW<USSS>
JTTK >'/ -<C' ''0.$*))'0.$$'$/4) /*'$./$  #1$*0- $)
(( -.$1 $-/0')1$-*)( )/.<D!%$ %!! +1*'>VYW<)*>TXVX
++>VXW\?VXXZ<USS\>
JTUK > '/ -< > +)')"< )>*-*($).< C$(0'/$)" $-/0' )1$-*)( )/.
2$/#$) $-/0' )1$-*)( )/. . /# .$.!*-  .4#*+#4.$. *! - . ) <D
$ %&! %! $"%././+1*'>U\<)*>V<++>+ -=\U<
USTS>
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
UU
).00$.!$)$.#$)"#./0 )//)$1 -.$/4*'' " *)*)>$.$)/ - ./.$)'0 
- '?/$( "'*'$''0($)/$*)*)/# < .+ $''4 .  *) .+# -$' #-(*)$.>
  #. )  $) $.$*)< ("$)" ) $-/0' )1$-*)( )/. HI !-*( /# 
 +-/( )/*!*(+0/ -$ ) <)$1 -.$/4*'' " *)*)<).0($// #$.#
/# .$. *) /#  /*+$ *! "'*' $''0($)/$*) $) 0)  USTT>   )   *)//  /
$>40Q.>0'>>0&>
 +-/( )/*!*(+0/ -$ ) 
)$1 -.$/4*'' " *)*)
*2 -/- /
*)*)TY<>
 .+ -*-/ ). )$. )$*--+#$. 9)"$) -/  *( -$. />2*-&$)"*)
- '?/$(  "'*' $''0($)/$*) !*- /#  "( . $)0./-4> $. - . -# $)/ - ./ $.
- ) -$)"'"*-$/#(.) +-/$0'-'4"'*'$''0($)/$*)> #.) $)$.$*)<
("$)" ) $-/0' )1$-*)( )/. !-*( )$1 -.$/4 *'' "  *)*)>   2.
2- #*)/# /*+$*!"'*'$''0($)/$*)/)$1 -.$/4 *'' "  *)*) $)
USTT>
 *( -$./>
$/4*0. 
TUY?TVS$''.*
(-$" 
UT
 '=^WWHSITUUVWXSTZS
3=^WWHSITUUVVYTVYU
($'=% .+ -Q" *( -$.>*(
)&% #)) 0-- )/'4 2*-&. .  *).0'/)/ $) /#  !$))$' . -1$ . )
($)/$).'$)&./* ($.)*)*--4 . -# ''*2 / )$1 -.$/4*'' " 
*)*)> ($)/$).) $)/ - ./ $)"'*'$''0($)/$*)<- '?/$( +#4.$''4?. 
- ) -$)"<)1$-/0'- '$/4> ) *)// /+>&#))Q.>0'>>0&>
 +-/( )/*!*(+0/ -$ ) 
)$1 -.$/4*'' " *)*)
*2 -/- /
*)*)TY<>
 ''/ -$.  . -#-*! ..*-//# )$1 -.$/4*! - '*)< +$)<)
-*! ..*- *! $-/0' )1$-*)( )/.< )$1 -.$/4 *'' "  *)*)< > $. - . -#
$)/ - ./.$)'0 1$-/0'- '$/4)$/.++'$/$*).$)+.4#*'*"4)) 0-*.$ ) >
  #.   !-*( )$1 -.$/4 *! *)*) ) #  )   *)//  /
( '.'/ -Q0> 0>
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
UV

)$1 -.$// - '*)
0'// .$*'*"$<
 +-/( )/  -.*)'$//<1'0$7$-/( )/..$*'6"$.<
(+0. 0) /?$!$$ /- <
.. $" '''P -*)TZT<
S[SVX- '*)
+$)
 '=^VW\VWSV\YT[
($'=( '.'/ -Q0> 0
Digital Object Indentifier 10.1109/MCG.2011.69 0272-1716/$26.00 2011 IEEE
This article has been accepted for publication in IEEE Computer Graphics and Applications but has not yet been fully edited.
Some content may change prior to final publication.
... In the only study where the congruency of an auditory stimulus with a visual stimulus was explored, no significative impact on the SoE was found [18]. The realism of sensorial feedback seems to enhance more realistic responses of the participants that are exposed to it [15,44,64]. In a case study, the exposure of an SCI patient to a very realistic immersive virtual environment combined with auditory and thermal stimuli consistent with the scenario and with tactile vibratory stimuli coherent with the action (walking) has been shown to provide high levels of SoE [15]. ...
... Nevertheless, both conditions seem to induce high scores of SoA that do not differ significantly from each other. Also, in another study in which the MI-BMI task consisted in popping virtual balloons with virtual hands or with The realism of sensorial feedback seems to enhance more realistic responses of the participants that are exposed to it [15,44,64]. In a case study, the exposure of an SCI patient to a very realistic immersive virtual environment combined with auditory and thermal stimuli consistent with the scenario and with tactile vibratory stimuli coherent with the action (walking) has been shown to provide high levels of SoE [15]. ...
Sensorial Feedback Contribution to the Sense of Embodiment in Brain–Machine Interfaces: A Systematic Review
Article
Full-text available
  • Dec 2023
The sense of embodiment (SoE) is an essential element of human perception that allows individuals to control and perceive the movements of their body parts. Brain–machine interface (BMI) technology can induce SoE in real time, and adding sensory feedback through various modalities has been shown to improve BMI control and elicit SoEe. In this study, we conducted a systematic review to study BMI performance in studies that integrated SoE variables and analyzed the contribution of single or multimodal sensory stimulation. Out of 493 results, only 20 studies analyzed the SoE of humans using BMIs. Analysis of these articles revealed that 40% of the studies relating BMIs with sensory stimulation and SoE primarily focused on manipulating visual stimuli, particularly in terms of coherence (i.e., synchronous vs. asynchronous stimuli) and realism (i.e., humanoid or robotic appearance). However, no study has analyzed the independent contributions of different sensory modalities to SoE and BMI performance. These results suggest that providing a detailed description of the outcomes resulting from independent and combined effects of different sensory modalities on the experience of SoE during BMI control may be relevant for the design of neurorehabilitation programs.
View
... Entertainment, education and training (Hvass, J., et al. (2017); Lee, J.,et al (2019); Bian, Y., et al (2016);Cooper, N., et al.,(2018); Cowan, K. and S. Ketron, (2019); David, D., et al.(2019); Kim, D. and Y.J. Ko,(2019), Ahir, K., et al., (2019); Christian, M. et al. (2017), Pagano, A., et al.(2020), Ferguson, C.,et al (2020). journalism and tourism (Shin and Bioca, (2018) ;Peña, et al (2010) ;Errichiello, et al. (2019) ;Huang, et al., (2016); Kim, and Hall (2019) technical and psychological understanding (Witmer et al,(2015); Witmer, and Singer, (2018); Yu, I., et al.(2012); Garau, M., et al.,(2008) ;Skarbez, et al.(2017b); Terkildsenand Makransky(2019); Usoh, M., et al.(2000); Slater, and. Wilbur,(1997) ;Slater, et al(2006) ;Slater,(2009) ;Slater,(2018);Vinayagamoorthy et al,(2008) ;Schubert,et al (2001);Tcha-Tokey, K., et al.,(2016) ;Hudson, et al.(2019) and other areas keep investing in research to establish best practices to improve the UX in IVR. ...
Assessing User Experience in Immersive Virtual Reality Environment: A review of interconnected terms and meanings
Article
Full-text available
  • May 2024
This article reports a research project aiming to identify aspects that influence User Experience (UX) in Immersive Virtual Reality (IVR) environments.
View
... It can relate, for example, among others, to the acting of the characters in the story and them being perceived as autonomous sentient entities instead of artificial contraptions that seem to be programmed to act in specific ways [18]. Interestingly, Psi is not related to photorealism or the quality of computer graphics, as even cartoony representations can elicit it [20], though it has been shown that realistic rendering is more likely to result in higher levels of Psi [21]. PI and Psi together are generally referred to as presence, and it has been shown that VR can elicit stronger sense of presence and stronger emotional responses compared to traditional forms of media [22]. ...
Cultivating empathy through narratives in virtual reality: a review
Article
Full-text available
  • May 2024
  • PERS UBIQUIT COMPUT
In recent years, there has been a growing interest in the potential of virtual reality (VR) as a powerful tool for storytelling and as a means of promoting empathy. This systematic review examines 20 research papers that were deemed relevant based on inclusion and exclusion criteria from a database of a total of 661 papers to investigate the use of VR for empathy-building through immersive storytelling. Thematic analysis of the interventions revealed that most of the narratives focused on the experiences of victims of abuse, social minorities, and individuals affected by medical conditions or political ramifications. These fall under three types of digital narratives identified as (a) personal, (b) historical, and (c) educational. Changes in empathy are identified either through comparisons with non-VR narratives or pre- and post-interventions. Interaction techniques, VR affordances, and methods to measure empathy are further identified. The review concludes that while VR shows promise as a tool for promoting empathy, more research is needed to fully understand its potential and limitations.
View
... Scholars discussed factors such as conforming to users' expectations, and adequate, non-lagging viewpoint changes (Sutcliffe and Gault, 2004), and including virtual objects, sounds, and scenes as part of what a user will consider when judging the level of "realism". Some work argues that perceived "realism" depends on the physiological state of the user and not on the application's graphics quality (Lipp et al., 2023;Molina et al., 2020;Yu et al., 2012). ...
Autobiographically Designing Mixed Reality for Lecturers
Conference Paper
Full-text available
  • May 2024
The implementation of educational artefacts based on new technologies depends on the skills and motivation of lecturers in the field. Aside from early adopters, lecturers often rely on best practices and exemplifications for their specific subject of teaching. In this work, we present how we applied end-user programming tools for Mixed Reality and the area of technical drawing, construction, and Computer Aided Design. With this approach, we created MACARONI, a Mixed Reality technical drawing section view tool. In an expert user study, we collected insights on how lecturers at our institution perceive Mixed Reality as teaching tool, exemplified by MACARONI. Also, based on the evaluation of our solution by the participating lecturers, we reflect on autobiographical design for the purpose of tapping in technologies for others. We argue that it helps to showcase the technology and how it can be applied for those lecturers, who did not consider using the technology before.
View
... It is assumed that realism is a crucial factor for task performance. The issue is that a simple increase in graphical quality not always results in the perception change [8,11,16,17,19]. Nowadays, it is commonly known that a user's assessment of VR realism is related not only to a level of immersion and textures and lighting quality, but also to presence, user's expectations, and previous experience [1,18]. ...
Are You Aroused Enough to See the Difference? The Role of Physiological Arousal in Perceiving Realism of Virtual Scene
Conference Paper
Full-text available
  • Oct 2023
Simulation realism is a crucial factor for task performance in virtual reality. The issue is that it does not simply result from a simulation's graphical quality and is often connected to users' expectations and the capacity of the cognitive system. It is assumed that perceived realism may be affected by physiological arousal which is the basis of emotional reactions and of attention prioritizing. The main aim of the presented study is to verify whether perceptual characteristics of a virtual scene – complexity and vividness of virtual objects – affect perceived realism. The secondary aim is to test whether realism assessment changes because of arousal. An experimental study was conducted with 100 participants in total. Four experimental groups differ in terms of the complexity of a virtual scene (i.e., number of objects in the field of view) and vividness of virtual objects (i.e., figure-ground contrast). Participants were asked to perform a task, that was taking on the role of a marshaller and positioning the plane on the airport apron in the virtual reality simulation. During the task, electrodermal activity was measured. After the virtual session, participants assessed perceived realism. Results indicate that the complexity and vividness of virtual scene do not affect perceived realism directly. Physiological arousal (i.e., skin conductance level) is a moderator of the relationship between the vividness of the virtual scene and perceived realism. A high level of arousal increases realism assessment in vivid simulations.
View
... However, Slater et al. [22] could not separate the effects of the increase of the illumination quality from the dynamic real-time shadows and reflections. Yu et al. [23] in a follow-up study aimed to fill that gap. The authors compared three scenes, one baseline without dynamic shadows and reflections, one with local illumination using interpolated shading, and another with global illumination. ...
View
View
A Methodological Approach for Unveiling the Evolution of Frescoes Through a Virtual Reality
Conference Paper
  • Oct 2024
Virtual Reality (VR) technologies offer a break-through in overcoming architectural barriers, enabling users to visualize and interact with otherwise inaccessible places. This paper explores the application of VR, particularly in the context of Matera Sassi's rock churches. Due to the irregular structure of the site, traditional exploration methods pose challenges, especially for individuals with motor disabilities. Using the Unreal Engine 5.2 game engine and digital photogrammetry, we reconstruct and explore 3D models of rock churches, focusing on fresco details for high-quality mesh generation. To enhance realism, we incorporate virtual avatars of real experts using motion capture systems for lifelike animations. Furthermore, our application supports remote, real-time user interactions, enabling immersive experiences via Head Mounted Displays (HMDs) such as the HTC Vive Focus 3. To assess this application, user studies with specialists were conducted to gather feedback on usability and sentiment, demonstrating the potential of VR in promoting accessibility and cultural heritage analysis.
View
View
View
Simulating Virtual Environments within Virtual Environments as the Basis for a Psychophysics of Presence
Article
Full-text available
  • Jul 2010
A new definition of immersion with respect to virtual environment (VE) systems has been proposed in earlier work, based on the concept of simulation. One system (A) is said to be more immersive than another (B) if A can be used to simulate an application as if it were running on B. Here we show how this concept can be used as the basis for a psychophysics of presence in VEs, the sensation of being in the place depicted by the virtual environment displays (Place Illusion, PI), and also the illusion that events occurring in the virtual environment are real (Plausibility Illusion, Psi). The new methodology involves matching experiments akin to those in color science. Twenty participants first experienced PI or Psi in the initial highest level immersive system, and then in 5 different trials chose transitions from lower to higher order systems and declared a match whenever they felt the same level of PI or Psi as they had in the initial system. In each transition they could change the type of illumination model used, or the field-of-view, or the display type (powerwall or HMD) or the extent of self-representation by an avatar. The results showed that the 10 participants instructed to choose transitions to attain a level of PI corresponding to that in the initial system tended to first choose a wide field-of-view and head-mounted display, and then ensure that they had a virtual body that moved as they did. The other 10 in the Psi group concentrated far more on achieving a higher level of illumination realism, although having a virtual body representation was important for both groups. This methodology is offered as a way forward in the evaluation of the responses of people to immersive virtual environments, a unified theory and methodology for psychophysical measurement.
View
An Experiment on Public Speaking Anxiety in Response to Three Different Types of Virtual Audience
Article
Full-text available
  • Feb 2002
This paper describes an experiment to assess the anxiety responses of people giving 5 min. presentations to virtual audiences consisting of eight male avatars. There were three different types of audience behavior: an emotionally neutral audience that remained static throughout the talk, a positive audience that exhibited friendly and appreciative behavior towards the speaker, and a negative audience that exhibited hostile and bored expressions throughout the talk. A second factor was immersion: half of the forty subjects experienced the virtual seminar room through a head-tracked, head-mounted display and the remainder on a desktop system. Responses were measured using the standard Personal Report of Confidence as a Public Speaker (PRCS), which was elicited prior to the experiment and after each talk. Several other standard psychological measures such as SCL-90-R (for screening for psychological disorder), the SAD, and the FNE were also measured prior to the experiment. Other response variables included subjectively assessed somaticization and a subject self-rating scale on performance during the talk. The subjects gave the talk twice each to a different audience, but in the analysis only the results of the first talk are presented, thus making this a between-groups design. The results show that post-talk PRCS is significantly and positively correlated to PRCS measured prior to the experiment in the case only of the positive and static audiences. For the negative audience, prior PRCS was not a predictor of post-PRCS, which was higher than for the other two audiences and constant. The negative audience clearly provoked an anxiety response irrespective of the normal level of public speaking confidence of the subject. The somatic response also showed a higher level of anxiety for the negative audience than for the other two, but self-rating was generally higher only for the static audience, each of these results taking into account prior PRCS.
View
A Virtual Presence Counter
Article
Full-text available
  • Oct 2000
This paper describes a new measure for presence in immersive virtual environments (VEs) that is based on data that can be unobtrusively obtained during the course of a VE experience. At different times during an experience, a participant will occasionally switch between interpreting the totality of sensory inputs as forming the VE or the real world. The number of transitions from virtual to real is counted, and, using some simplifying assumptions, a probabilistic Markov chain model can be constructed to model these transitions. This model can be used to estimate the equilibrium probability of being “present” in the VE. This technique was applied in the context of an experiment to assess the relationship between presence and body movement in an immersive VE. The movement was that required by subjects to reach out and touch successive pieces on a three-dimensional chess board. The experiment included twenty subjects, ten of whom had to reach out to touch the chess pieces (the active group) and ten of whom only had to click a handheld mouse button (the control group). The results revealed a significant positive association in the active group between body movement and presence. The results lend support to interaction paradigms that are based on maximizing the match between sensory data and proprioception.
View
The Use of Virtual Reality in the Study of People's Responses to Violent Incidents
Article
Full-text available
  • Dec 2009
This paper reviews experimental methods for the study of the responses of people to violence in digital media, and in particular considers the issues of internal validity and ecological validity or generalisability of results to events in the real world. Experimental methods typically involve a significant level of abstraction from reality, with participants required to carry out tasks that are far removed from violence in real life, and hence their ecological validity is questionable. On the other hand studies based on field data, while having ecological validity, cannot control multiple confounding variables that may have an impact on observed results, so that their internal validity is questionable. It is argued that immersive virtual reality may provide a unification of these two approaches. Since people tend to respond realistically to situations and events that occur in virtual reality, and since virtual reality simulations can be completely controlled for experimental purposes, studies of responses to violence within virtual reality are likely to have both ecological and internal validity. This depends on a property that we call 'plausibility' - including the fidelity of the depicted situation with prior knowledge and expectations. We illustrate this with data from a previously published experiment, a virtual reprise of Stanley Milgram's 1960s obedience experiment, and also with pilot data from a new study being developed that looks at bystander responses to violent incidents.
View
Place Illusion and Plausibility Can Lead to Realistic Behaviour in Immersive Virtual Environments
Article
Full-text available
In this paper, I address the question as to why participants tend to respond realistically to situations and events portrayed within an immersive virtual reality system. The idea is put forward, based on the experience of a large number of experimental studies, that there are two orthogonal components that contribute to this realistic response. The first is 'being there', often called 'presence', the qualia of having a sensation of being in a real place. We call this place illusion (PI). Second, plausibility illusion (Psi) refers to the illusion that the scenario being depicted is actually occurring. In the case of both PI and Psi the participant knows for sure that they are not 'there' and that the events are not occurring. PI is constrained by the sensorimotor contingencies afforded by the virtual reality system. Psi is determined by the extent to which the system can produce events that directly relate to the participant, the overall credibility of the scenario being depicted in comparison with expectations. We argue that when both PI and Psi occur, participants will respond realistically to the virtual reality.
View
Visual Realism Enhances Realistic Response in an Immersive Virtual Environment
Article
Full-text available
  • May 2009
Does greater visual realism induce greater participant presence in immersive virtual environments (VE)? Presence refers to how realistically participants respond to the environment as well as their subjective sense of being in the place depicted by the VE. Thirty-three people were exposed for three minutes to a virtual environment depicting a precipice using a head-tracked head-mounted display system. Seventeen of them saw the environment rendered with real-time recursive ray tracing (RT) that included shadows and reflections of their virtual body, and the remainder experienced the same environment rendered with ray casting (RC), which did not include shadows and reflections. Participants completed a presence questionnaire immediately after their experience, and physiological responses (skin conductance and electrocardiogram) were recorded throughout. Results show that subjective presence was higher for the RT environment than for the RC one and that higher stress was induced in the RT environment compared to the RC one.
View
Real-Time Global Illumination for VR Applications
Article
Full-text available
  • Jan 2009
Real-time global illumination in VR systems enhances scene realism by incorporating soft shadows, reflections of objects in the scene, and color bleeding. The Virtual Light Field (VLF) method enables real-time global illumination rendering in VR. The VLF has been integrated with the Extreme VR system for real-time GPU-based rendering in a Cave Automatic Virtual Environment.
View
From presence to consciousness through virtual reality
Article
Full-text available
  • May 2005
  • NAT REV NEUROSCI
Immersive virtual environments can break the deep, everyday connection between where our senses tell us we are and where we are actually located and whom we are with. The concept of 'presence' refers to the phenomenon of behaving and feeling as if we are in the virtual world created by computer displays. In this article, we argue that presence is worthy of study by neuroscientists, and that it might aid the study of perception and consciousness.
View
The Irradiance Volume
Article
Full-text available
  • Apr 1998
A major goal in computer graphics is realistic image synthesis. To this end, illumination methods have evolved from simple local shading models to physically based global illumination algorithms. Local illumination methods consider only the light energy transfer between an emitter and a surface (direct lighting), while global methods account for light energy interactions between all surfaces in an environment, considering both direct and indirect lighting. Even though the realistic effects that global illumination algorithms provide are frequently desirable, the computational expense of these methods is too great for many applications. Dynamic environments and scenes containing a very large number of surfaces often pose problems for global illumination methods. This article presents a different approach to calculating the global illumination of objects. Instead of striving for accuracy at the expense of performance, we rephrase the goal: to achieve a reasonable approximation with high performance. This places global illumination effects within reach of many applications in which visual appearance is more important than absolute numerical accuracy
View
What It Is Like To See: A sensorimotor theory of perceptual experience
Article
  • Oct 2001
The paper proposes a way of bridging the gapbetween physical processes in the brain and the ''''felt''''aspect of sensory experience. The approach is based onthe idea that experience is not generated by brainprocesses themselves, but rather is constituted by theway these brain processes enable a particular form of''''give-and-take'''' between the perceiver and theenvironment. From this starting-point we are able tocharacterize the phenomenological differences betweenthe different sensory modalities in a more principledway than has been done in the past. We are also ableto approach the issues of visual awareness andconsciousness in a satisfactory way. Finally weconsider a number of testable empirical consequences,one of which is the striking prediction of thephenomenon of ''''change blindness''''.
View