Using a Floating Origin to Improve Fidelity and Performance of
Large, Distributed Virtual Worlds
School of Computer Science and Software Engineering
The University of Western Australia
Large Virtual Worlds (VWs) are increasingly
common in the computer graphics areas of simulation,
games, geospatial or scientific visualisation. In such
VWs, simulated motion of the viewpoint and other
objects becomes jittery and lacking in realism when
far from the world's origin. Shape and appearance of
objects can also degenerate. Since these effects
depend on position in space, they will be collectively
termed Spatial Jitter (SJ).
Traditional solutions to SJ embody the idea that
viewpoint motion through the VW must involve a
change of the viewpoint's coordinates. This notion of
viewpoint motion increases design complexity and the
processing overhead of code written to counter SJ.
A Floating Origin (FO) approach is presented
which floats the world's origin with the viewpoint
when navigating a continuous VW, eliminating SJ
effects and lowering design and processing overheads.
It ensures constant high fidelity in contrast to the
continuously varying fidelity of conventional solutions.
Imagine yourself at the top of a ramp leading down
and away into the distance. It seems mirror smooth
but as you walk down, small irregularities appear like
tiny staircase steps. Further down your progress gets
quite bumpy. Eventually your feet can fit comfortably
on each step. Later, you have to take small jumps. You
conclude that before long the next step will result in a
fall and perhaps broken bones!
The diabolical staircase with ever larger steps
represents the floating point number line, with its origin
at the top and ever increasing gaps between one
representable number and the next. On a digital
computer, there is a discrete set of representable
floating point numbers which are not distributed
evenly : the gap between one number and the next
increases with its size, or distance from the origin. The
gap between 1 and the next number is called the
machine epsilon, Em . The gap between x and the
next number is ~ x . Em. In general,
gap = P2(x) . Em , where P2(x) is the largest power
of 2 that is less than |x|.
In a VW, the position of objects is defined by
coordinates, a notation that denotes distance from
origin . Modern computer graphics hardware uses
floating point numbers for the coordinates of objects
[4,16]. Therefore, like the staircase, the further
coordinates are from the origin the larger the gaps
It follows from the above that moving something
from one position to another will show increasingly
larger jumps with increasing distance from origin,
leading to SJ. Figure 1 illustrates the jittery motion of
two dots moving far from the origin. SJ effects have
been noted before [1, 9, 13, 18, 26, 27, 28, 29].
The total number of representable values a floating
point number can have depends on the precision  of
the floating point representation used. In general, the
precision of a real number is the number of decimal
Figure 1. Snapshots of two moving dots overlaid
into one image. The dots are near (1000000,
1000000, 1000000) and move from the distant
upper right to the near lower left. Each upper dot
snapshot is connected by a line, tracing its jittery
path. A straight line underneath highlights the
uneven motion of the dots.
digits in it which are treated as significant for
computations . Current graphics hardware has a
maximum of 23 bits precision, the precision of the
Single Precision Floating Point (SPFP) standard ,
for the coordinates of objects. Often, the precision used
can be less  and a lower precision means larger gaps
Poor understanding of SJ and its cause, and
difficulty grasping the idea of moving the origin instead
of the viewpoint, have been barriers to implementing a
FO solution. Another barrier has been that existing
designs can be difficult to convert to a FO approach.
Consequently, this paper aims to remove the enigma
surrounding the SJ problem by explaining it clearly and
further aims to show how an optimal and complete
solution can be attained.
In order to better explain different approaches to
preventing SJ, the VW application is divided into a
display system (DS) and object system (OS). The OS is
responsible for defining, tracking and handling the
interaction of objects. These objects are given to the
DS which generates a user's view into the VW
(rendering). The DS uses a representation of the
objects in a form more suitable to fast rendering and
has operators that affect object appearance. Among the
operators are transforms which shift objects so they are
positioned correctly in relation to each other.
The following describes how SJ has been addressed
and how some people had difficulties understanding the
problem. The FO approach is then described with
emphasis on how designers need to change the way
they think about SJ and the solution. The general
design for a distributed FO system is presented and
compared with conventional solutions. The discussion
also describes how the FO method should be combined
with level of detail streaming and dynamic placement
to complete the approach. The benefits of FO are
summarised in the concluding remarks.
2. Traditional approaches
Traditional approaches to SJ fall into three classes:
on-the-fly shifting of coordinates, subdivision of the
world into local coordinate systems and piecewise
shifting of world coordinates (WC).
2.1. On-the-fly shifting of coordinates
The on-the-fly approach to jitter shifts objects and
the viewpoint close to the origin before calculations are
performed that will noticeably affect how they are
rendered. The shifting involves changing the object
coordinates or transforms that affect their coordinates.
In an article on simulating a solar system, Oneil 
describes dealing with jitter by shifting visible objects
just before they are rendered to each frame. A frame is
an image in a series sent to the user's display at a rate of
at least 30 frames per second to give the appearance of
smooth animation. Oneil's algorithm temporarily sets
the viewpoint position at the world origin and subtracts
the true viewpoint position from that of all visible
objects. Thus everything used in rendering a frame now
has small, accurate coordinates and the calculations are
consequently higher fidelity, avoiding jitter effects.
Once the frame is rendered, viewpoints and object
positions are restored to their previous values.
Other on-the-fly examples can be found in online
articles and forums on game development sites [26, 27,
28, 29]. For example, in the blitzcoder forum ,
“Andy” proposed a periodic on-the-fly method: every
time the viewpoint became, for example, 10,000 from
the origin, it was shifted back to the origin and all
objects were shifted by the same transform to keep
them in correct relative position.
2.2. Multiple local coordinate systems
Many VWs were divided into smaller coordinate
regions enabling easier management of detail and
minimizing jitter at the same time. This segmentation
requires additional structures and management
overhead to handle movement between regions.
The Dungeon Siege game segmented its world into
SiegeNodes, each with its own local coordinate space.
When the viewpoint crossed a boundary between
nodes, the local coordinate system changed to that of
the node being entered and a “Space Walk” began .
The space walk visited each active node and
recalculated coordinate transforms to shift objects
closer to the new local origin. This ensured coordinates
did not get large enough to cause jitter.
The connection between nodes in Dungeon Siege
was similar to what has been called portals in other
segmented VWs. Eternal Lands (EL), a Massively
Multiplayer Online Game (MMPOG), used portals
which teleported the player from one segment to
another. EL had one world map divided into continent
maps. It also used ships as a natural transporter system.
Other games also made use of natural transporter
systems to move between segments [12, 15, 31].
In the Morrowind game , a player walking far
enough along a path would experience a halt where
movement was temporarily blocked, while a message
like “loading external environment” was displayed.
This hiatus marked the transition from one segment of
the game world and the next.
Flight simulators need to counter jitter because they
cover very large areas. FlightGear, for example,
divided the earth into tiles, each with a local coordinate
system. It made aircraft and other object coordinates
relative to the reference point of the tile they were in.
“This reference point (for purposes of avoiding floating
point precision problems) defines the origin of a local
coordinate system” .
Another simulation system using local coordinate
spaces was Spline, used by Barrus et al.  to build the
Diamond Park virtual world. Spline supported the
subdivision of the larger world into smaller locales and
the efficient communications between them. When an
object moved from one locale to the next its
coordinates were transformed to be relative to the new
VGIS, a GIS application for modeling the earth,
subdivided the world into regions. VGIS was described
in a paper by Lindstrom et al.  who thought the
subdivision was necessary: “This is necessary as the
precision afforded by current graphics hardware is
insufficient for representing detailed geometry
distributed over a large volume in a single coordinate
2.3. Piecewise shifting of coordinates in a
continuous virtual world
Dungeon Siege appears like a continuous world
because there is no noticeable hiatus while moving
between segments, but it is not a true continuous world
because it subdivided the world into SeigeNodes. A
true continuous world has a single world coordinate
system with no artificial segmentation of that space.
Examples of applications built on a continuous world
space are Terravision , planet-earth  and
applications using the GeoVRML  technology.
These applications perform a shift when a special type
of viewpoint is selected.
GeoVRML is a geospatial extension to the VRML
 language. In GeoVRML, whenever one moves to a
new area of interest, a GeoViewpoint is used. A
GeoViewpoint contains the origin of the area of interest
and the position of a nearby viewpoint, both in WC.
The GeoViewpoint reverse transforms the world by
subtracting the origin from the WC of the nearby
viewpoint and other objects resulting in small
coordinate values, thus avoiding jitter. In this way, the
world is shifted in a piecewise fashion as the user goes
from viewpoint to viewpoint.
Apart from viewpoint selection, another way to
move though a virtual world is by free navigation. Free
navigation is when the user operates controls for
walking, flying or other continuous movement. In
GeoVRML, there is nothing to stop one from freely
navigating to a point where SJ occurs. Terravision is
based on GeoVRML and thus has the same properties,
except the free navigation issue is managed by
periodically re-translating the world so the viewpoint is
at the origin, and everything else is closer to it.
The planet-earth project  uses a continuous
shifting of the world. This is a combination of
piecewise shifting via viewpoints like GeoVRML and
TerraVision plus continuous reverse translation of the
world during free navigation. The latter is what
distinguishes the FO method from other continuous
world methods like GeoVRML and TerraVision and is
described in the next section. It also distinguishes FO
from the traditional SJ solutions which have the
viewpoint always moving relative to the origin.
3. Floating origin approach
3.1. Reversal of navigation thinking
In the review of traditional systems that manage
jitter, there is a common thought process apparent in
their design. The apparent assumption is that while
freely navigating or moving from one viewpoint to
another, the coordinate of the viewpoint must move
through the virtual world: i.e. its value must change.
Coordinate shifting is only added on just prior to
rendering frames or to periodically reduce the
viewpoint and object coordinate values. Even with
GeoVRML and TerraVision, free navigation moves the
viewpoint through the world space.
The FO approach is a departure from such
conventional navigation thinking. As shown in Figure
2, instead of allowing the viewpoint to move in the
world, the world is reverse transformed to position the
desired point at the origin. The origin is not fixed
relative to the rest of the world but floats with the
viewpoint. Therefore, the viewpoint is always centered
at the highest fidelity place: the origin, even when
freely navigating. The effect of using a FO is that there
will be no observable SJ. Since the origin is the world's
center, this type of viewpoint is termed here a centered
3.2. Understanding the problem, grasping the
solution and implementing it
Comprehensive searches revealed the closest
approaches to FO that have been formally documented
are the GeoVRML and Terravision approaches already
Figure 2. Comparing conventional and floating
described [9, 18]. They are in the narrow field of web
based geospatial 3D. There were also a small number
of online articles and forum topics [13, 26, 27, 28, 29].
This section looks at how people came to understand
SJ and their approaches to it.
In the informal online documentation, there is
evidence people have had difficulty understanding the
problems caused by large distances from the origin. On
the blitzcoder community forum , “Nukomod”
initially did not understand what floating point
coordinates and distance from origin would do to
motion and rendering: “The further a mesh travels from
the 0,0,0 origin the more it begins to 'break apart'.
There seems to be some inaccuracy in positioning child
entities and the whole model begins to 'shake'.”
In the BlitzBasic forum, “Second Chance”  had
a problem with disappearing planets in a space game:
“...Then it's assigned its orbital distance from the star
(0,0,0). Everything looks good until you get out to
about the orbit of Uranus (29,000,000 game units) and
beyond, at that point the planets start to wink in and out
In a gamedev.net forum, “Lode”  was surprised
by a problem with rendering planets in a space game: “
... just to test I made some cube-planets, and even if
they're only 1000 units they're uglier than the EXACT
same scene 1000 times smaller! ... for bigger scenes
with more cubes at larger distances, it looks even worse
In another blitzcoder forum topic, “Nmuta”  had
similar problems with objects 10,000 units along the z
axis: “Anyone else hear about this problem occurring
if you don't normalizing your world regularly, and
getting graphics problems when you go too far away
from 0,0,0 ? I need to know what that means.”
The above quotes show that people working on
large scale worlds can be surprised when encountering
the limits of floating point coordinates and are initially
at a loss as to what to do about it.
There is even evidence that once people understood
the jitter problem and a general solution: that
viewpoint and object coordinates should be closer to
the origin, they still had difficulty grasping the FO
concept. For example, on the blitzcoder forum ,
Nmuta says: “ It's just weird, the thought of it. Instead
of moving a person, you are moving several tons of
land and buildings and enemies!!!! ... The whole
concept of 3D in general is such an interesting
illusion”. “Mt Dew” says: “When first suggested to me
that I needed to change my system from moving my
person through the solar system to moving the solar
system around the person ... well ... i was a bit
daunted”. “Andy” stated: “This is probably the single
most difficult concept for new programmers to
understand, but it is vital to the process.”
Leclerc et al. and Reddy et al. [9,18] understood SJ
and created the piecewise continuous world solutions
of GeoVRML and TerraVision. However, they did not
take the method to a full FO solution. Since these
authors published in a fairly narrow field, this might
explain why their understanding did not disseminate to
the broader community and reach the games and flight
The lack of adequate, widespread literature on the
subject and evidence of difficulty thinking of a solution
in terms of continuous reverse transformation are the
main motivations for writing this paper. The following
section describes the design for FO navigation.
3.3. Design for floating origin navigation and
To implement FO navigation, the design of the
client needs to support reverse transformation of the
world whenever the viewpoint is set to a WC and
during free navigation. This section describes a general
distributed architecture to meet these requirements.
As shown in Figure 3, reverse transforming the
world can be achieved by placing a top level transform,
the world transform (WT), over the entire set of objects.
Whenever a viewpoint is selected, the inverse of the
viewpoint's coordinate is applied to the WT. The result
is that the objects are shifted in reverse towards the
viewer who stays at the origin.
Figure 3. Structure of the client, showing how
centered viewpoint and navigation components
affect the WT which, in turn, transforms objects.
Note how other navigation and behaviours do not
affect the WT but act directly on the objects.
Free navigation controls also apply a reverse
transformation to the WT. Other interaction and
behaviors, such as moving an object, opening a door, or
pressing a button, all happen in the normal fashion and
do not affect the WT.
A necessary consequence of the WT is that
viewpoints must not be under the WT itself because
this would form an endless feedback loop with the WT.
The design therefore separates viewpoints from the
objects and object transforms that are under the WT.
Normally, an application must keep track of where
objects are in relation to each other and to the user's
viewpoint in order to manage relationships and
interactions between objects and render things
correctly. However, in the FO approach, the object
coordinates in each user's DS are unique to that user's
position in the world because they are always the
smallest values relative to the user's current world
position. This is one reason why the OS part of the
application must be separate from the DS, so it can
keep track of viewpoint and object position in WC
while the DS separately transforms the local coordinate
system of each user. This also implies the application
has to keep track of a unique WT for each user.
A VW must be distributed to support multiple
participants, such as in a MMOG, distributed
simulation [2,11] or for collaboration. The OS
maintains the overall VW picture and oversees
interaction between participants, so it is the OS which
needs to be distributed, usually by putting part of it on
one or more servers. Similarly, distributing the FO
method is a matter of separating the OS into client and
server parts and defining a network communication
protocol to transmit the necessary information between
the parts (Figure 4).
It is the responsibility of each client DS to provide
position updates as the user navigates so the OS can
track positions in WC. In a distributed application, the
client's DS will pass its updated user position to its
local OS which now sends it on to the server OS. This
is similar to Massively Multiplayer Online Games
(MMOGs): the online servers must get user position
updates streamed back constantly in order to correctly
perform collision detection, physics and interactions
and update the visible picture for all users. The main
difference is that the server OS is keeping track of
reverse transforms for each user locale in addition to
tracking object users' WC positions.
Apart from changing the navigation code to reverse
transform the WT, the collision detection algorithm
may also need modifying. In a conventional system,
collision detection activates when navigation causes a
volume around the viewpoint to intersect with an
object. With FO, because the viewpoint does not move,
collision detection has to activate when an object is
moved to collide with the volume around the
In a VW, the user only needs to see the part of the
world in the vicinity of the current location. Therefore,
only detail from this part, the user's locale, need be
downloaded from server to client. That is no different
from MMOGs which already do similar management of
the amount of information the client system has to
handle and display. This management technique is
called Level of Detail (LOD) and not only limits the
information displayed but what has to be transformed.
In the FO approach, LOD would be streamed from
the server on demand to keep the overhead of changing
detail to a minimum as the user moves. In addition,
whenever a user selects a viewpoint the server will pass
the client the appropriate reverse transform to shift the
local DS's objects to the center of the locale. This
information may be in the form of a centered viewpoint
(Figure 2) or raw transform information.
Many objects such as terrain and other static things
do not have to exist in the DS until they are about to
become in visible range. Then they are placed
dynamically in the environment. This just in time
dynamic placement means objects are positioned with
optimum accuracy because their DS coordinates are
minimised to the smallest they can be before being
To transmit LOD, position and other information
between client and server, current distributed VW
applications commonly use TCP/IP sockets , or
UDP  for communication between client and
server. Some systems use multicast  and others use
HTTP . A combination of two of these methods is
also possible. The planet-earth project  uses HTTP
because it is widely supported and the fact that it
requires no setup effort for the user.
Figure 4. Architecture of the distributed VW
application showing separation of client and
server parts of the OS and how transformations
and position streaming is communicated.
Figure 4 shows the logical architecture of a
distributed VW application with the OS divided into
client and server components. Locale, LOD, transform
and position information is exchanged between the
server and client parts of the distributed OS. The client
OS applies reverse transforms to the visible world via
the DS, giving the user the impression of moving
through the world.
From this section, the following design aspects are
required to implement FO:
1. a top level transform, the WT, that affects all the
objects in the VW,
2. special centered viewpoints which reverse
transform the world through the WT,
3. a free navigation system that applies a reverse
transform to the WT,
4. separation of viewpoint transforms from object
structures in the DS,
5. distributing the OS between client and server
and providing a supporting protocol,
6. modified collision detection and terrain
7. streamed LOD, and
8. dynamic, just-in-time placement
4. Comparison of floating origin with
4.1 Design complexity and performance costs
There is a performance and design cost to traditional
solutions. Morrowind , for example, has a large
world divided into smaller parts. A player walking far
enough along a path will experience the hiatus
described in section 2. The delay is caused by the game
engine loading terrain and objects for a connecting
segment because the player has crossed one of the
invisible boundaries that separates segments. Apart
from causing a disruption to the immersive experience,
such events occupy the system resources enough to
make gameplay hesitate for a noticeable time.
Even though Dungeon Siege has no loading screens,
its space walk has significant performance costs. It
requires a scaffolding: a structure of linked nodes that
enable the walking algorithm to work its way out from
the new center node to other neighbors. It uses
considerable processing resources and the frequency of
performing recalculations has to be limited: “as
infrequently as possible to avoid bogging down the
CPU ” .
Algorithms like Oneil's also involve extra work to
modify the transformation for each object. Like other
graphics systems, Oneil's would require a structure
through which objects can be located in relation to each
other and the world. To transform each object the
structure has to be traversed to access each object's
transform. The work for transform calculations plus
scaffolding traversal is proportional to the number of
objects. Oneil's algorithm runs every frame, so, for a
large number of objects, would represent a large
processing overhead at a good frame rate (greater than
30 times a second).
In the blitzcoder forum , Andy said that with his
method, shifting all objects in one go is too
computationally expensive and would produce a
noticeable delay, so the algorithm was enhanced to
progressively shift objects, a small number at a time,
while allowing other operations to continue.
In contrast, the FO method does not need the
scaffolding and transform operations used by Dungeon
Siege, Oneil and others on every object, as the objects
are automatically translated via the WT. Therefore, a
lot of processing overhead is removed.
For viewpoint movement the reverse transformation
requires no additional code above what is normally
there because the navigation code that previously
transformed the viewpoint now (inversely) modifies the
WT instead. It is just the same operations applied in
reverse on a different place. Therefore, there is no
additional performance cost to using FO. This is the
same conclusion that Nmuta came to: Nmuta : “Yet
in terms of rendering, the computer doesn't really know
the difference I suppose. It would still be the same
number of polygons moving just as fast in the same
Although GeoVRML does not have the overhead of
transitions between segments because it uses a
continuous world, free navigation still allows the
viewpoint to move far from the origin where jitter can
occur and there is no automated control in place to
prevent it. There is also nothing stopping the
GeoViewpoint position being set to the other side of
the world to its origin, in which case jitter would be
very noticeable. The FO method does not separate
viewpoint position from the origin, thus eliminating
these potential problems.
4.2 Coordinate systems and representation
The FO method exploits the high fidelity region
around the origin of the floating point space used by
modern graphics systems. If other than floating point
was used, this would not be possible. Floating point
with a precision greater than 8 bits only came into wide
use in graphics hardware from 2002, when the Pixel
Shader 2.0 specification was released . Prior to
that, fixed point and integer numbers were commonly
used for coordinates and they have an even distribution
of representable numbers. Therefore, a FO approach
would not have benefited visualisation. This
background may also have contributed to the
difficulties some people had in understanding SJ and its
FO based solution on modern hardware.
There is no need for representing the coordinates of
objects and viewpoint in double precision floating
point as Oneil thought was necessary  because the
dense precision region around the SPFP origin gives
sufficient accuracy for smooth motion and accurate
rendering in VWs up to and larger than the earth .
Not having to use double precision for operations also
reduces processing overhead because SPFP operations
are faster than double precision operations .
Multiple local coordinate systems like in EL,
FlightGear and VGIS are also not required in an FO
approach. All supporting structures and algorithms to
handle transitions between segments, as in Morrowind,
Eternal Lands and Dungeon Siege are no longer
4.3 Applying a FO design
Despite its efficiency benefits, the FO method
cannot be fully exploited if the OS and DS are not
designed to support it. In online forums, there is
evidence that people attempted an approach similar to
FO but found it was not efficient to modify an existing
application. For example, Nmuta  tried using an
FO type of system to stop SJ with his space game, but
gave up and went with a an on-the-fly method when he
found the overhead of implementing FO on top of an
the B3D engine was too high: “keeping the player at
0,0,0 all the time as MSW suggested is proving to be a
little too tricky to implement given my current engine's
set up, so I think I might use your way, with the grid.”.
In the same forum “Andy” described the cost of
implementing FO on B3D, saying “You would end up
having to write code to do everything that B3D does
already and add overhead.”. He further said that the
progressive piecewise approach he proposed was only a
few lines of code but modifying B3D's “movement,
rotation and collision code will add hundreds of lines
and slow the program”.
From the above one can conclude that for a VW to
make best use of the efficiency of FO it would have to
be designed from the beginning with that method in
mind or already have a design that can be easily
As all of the conventional approaches to SJ allow
the viewpoint to move relative to the origin, accuracy
of motion and rendering will continually vary: i.e. the
fidelity will be unpredictable. Many developers may
not realise the cause when the quality of rendering is
subtly wrong when viewed from a large coordinate.
Small seams may appear in one place but not another.
Small unaccounted for inaccuracies could plague
developers who do not know they are simply caused by
SJ. FO ensures rendering is always performed from a
centered viewpoint and therefore ensures all motion
and rendering has the same quality.
The absence of complex scaffolding and code to
handle transitions from one local coordinate system to
the next results in a simpler design. As pointed out in
section 4.1, this simpler design has less processing and
code overhead, as long as the implementation is not
burdened by an existing code base with incompatible
One may sympathise with parents who complain the
younger generation are lazy: they expect everything to
come to them. In a virtual world the rules of physics do
not apply, it is just as easy to bring the world to you as
it is to move yourself in the world. This paper has
shown that for modern graphics hardware based on
floating point numbers, it is better to keep the
viewpoint at the origin and reverse transform the world.
So in terms of virtual worlds, the young have the right
way of thinking.
The problem of spatial jitter and several classes of
conventional approaches to the problem have been
described. The benefits of the floating origin solution
are that it:
1. eliminates observable spatial jitter,
2. lowers design complexity,
3. lowers processing overhead,
4. provides constant, optimum fidelity of motion
and rendering compared to the continually variable
fidelity of conventional approaches, and
5. allows end user devices to operate within their
precision limits without spatial jitter problems.
These benefits have to be weighed against the need
for a new design that will support floating origin
Floating point suits the view-centric nature of
computer graphics: the local region around the
viewpoint is what the user sees and that is where most
of the accuracy of rendering and motion needs to be. A
floating origin allows this natural benefit of floating
point to be applied to the rendering of every frame.
When combined with level of detail streaming and
dynamic placement a floating origin optimizes the
quality of motion, interaction and rendering throughout
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