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INTRODUCTION
!
This! research! introduces! and! presents! a! new$
algorithm$ named! “Trilateration$ Algorithm”! to! compute! the!
Geodetic!coordinates$ (ϕ,$ λ,$ h)$ of! any! point$ (P),! given! its!
Cartesian$ coordinates$ (xp,$ yp,$ zp)! in! reference! to! the! geodetic!
ellipsoid.!!
The! algorithm!is!based$ on$ the! new! “Seta-Point$
Theorem”! in! the! meridian$ plan,! which! defines!a!new!
deterministic$ Twin-Point$ (P0)$ for! any! point$ (P).! From! such! a!
Twin-Point! (P0),! a! single$ iteration$ solution! is! processed! to!
achieve$ highly-accurate$ values$ for! (ϕ,$ h)$ using! a! relatively!
simple$ and$ deterministic$ computational$ algorithm$ which! is!
both!valid!and!stable!for!all$values$of$(ϕ,$h).!!
The! proposed$ solution$ was! tested! on! a! sample! of!
4277$points.!The!mean$error$value!of!the!computed$latitude$is!
-2.291E-10$ arc-second! and! the! mean$ error$ value! of! the!
computed$height!is!3.96E-8$mm.!
!
!
!References$
$
• Featherstone,!W.,!&!Claessens,!S.!(2008).!Closed-form!transformation!between!geodetic!and!ellipsoidal!coordinates.!Studia!Geophysica!et!Geodaetica,!52(1),!1–18.!
• Ligas,!M.,!&!Banasik,!P.!(2011).!Conversion!between!Cartesian!and!geodetic!coordinates!on!a!rotational!ellipsoid!by!solving!a!system!of!nonlinear!equations.!Geodesy!
and!Cartography,!60(2),!145-159.!
• Heiskanen,!W.,!&!Moritz,!H.!(1967).!Physical!Geodesy.!San!Francisco:!Freeman!and!Co.!
Trilateration Algorithm To Transform Cartesian Coordinates Into Geodetic Coordinates
Mohamed ELEICHE(1,*) and Ahmed Hamdi MANSI(2,3)
(1) Faculty of Engineering, Egyptian Russian University, Cairo, Egypt; (*) Corresponding Author: mohamed.eleiche@gmail.com;
(2) Civil Engineering Department, College of Engineering, Shaqra University, Dawadmi, Saudi Arabia (ahmed.mansi@su.edu.sa);
(3) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Pisa, Italy (ahmed.mansi@INGV.it).
PROCESSING ALGORITHM
1. $Given$(r,$z)$and!required$(ϕ,$h):!
any!point$(P)$has!an!angle$(ϕ)!and!
a!height$(h)$above!the!reference!
ellipsoid;!!
2. Compute$the$Seta$Point$(W):!the!
Line$PW$crosses!the!ellipse!in!
point$(Qw);!
3. The! Line$ PW$ makes! an! angle$ (ϕw)$ with! a! horizontal$
distance$(hw)$from!point$(P)$to!the!intersection$(Qw);!
!
4. The! deterministic$ Twin-Point$ (P0),$
defined!by!(ϕw,$hw),!is!very!close!to!the!
point$(P).!
RESULTS and DISCUSSION
!
CONCLUSION
!
The! Seta-Point$ theorem$ provides! a! new$ trilateration$
algorithm$ for! the! conversion!of!Cartesian!coordinates! into!
Geodetic$coordinates.!!
The! computational$ requirements$ of! the! new! algorithm! are!
simple! and! do! not! exceed! the! solution$ of$ three$ quadratic$
functions$for!the!points!located!on!the!ellipse!surface.!!
The! algorithm!is!valid! for! all! values$ of$ geodetic$ and!
Cartesian$ coordinates.! Two$ iterations$ would! generate!
highly$accurate$geodetic$coordinates.!
1. Each!iteration!is!closer!to!the!true$value;!
2. The!relation!between!latitude!(ϕ)! versus!computational!
error!of!the!latitude$(ϕ-ϕw)$and!height$(h-hw).!
3. The!Boxplot!for!the!latitude$error!(ϕ-ϕw).!The!Seta-point!
is!at!the!left,!the!first!iteration!in!the!middle,!and!the!
third!iteration!at!right;!
4. The!Boxplot!for!the!height$error!(h-hw).!The!Seta-point!is!
at!the!left,!the!first!iteration!in!the!middle,!and!the!third!
iteration!at!right;!
• Pollard,!J.!(2002).!Iterative!vector!methods!for!computing!geodetic!latitude!from!rectangular!coordinates.!Journal!of!Geodesy,!60,!36-40.!
• Shu,!C.,!&!Li,!F.!(2010).!An!iterative!algorithm!to!compute!geodetic!coordinates.!Computers!&!Geosciences,!1145-1149.!
• Vermeille,!H.!(2002).!Direct!transformation!from!geocentric!coordinates!to!geodetic!coordinates.!Journal!of!Geodesy,!76,!451-454.!