[Proj] GGRS87 TO WGS84 PROBLEM(?)
Oscar van Vlijmen
ovv at hetnet.nl
Fri Dec 8 05:28:13 EST 2006
From: "Andreas T"
Date: Wed, 6 Dec 2006 23:44:19 +0200
Subject: [Proj] GGRS87 TO WGS84 PROBLEM(?)
> I have trouble trying to reproject a point from greek grid to WGS84.
> Supposing that these params are official and accepted enough,
I can't find better ones at the moment, so one might assume they're correct.
> // Projections declaration
> // Shape to be reprojected
> $myshape = ms_newpointobj();
> $myshape->setXY(552000, 4098077);
> The expected result (according to very reliable software like ArcGIS and
> others...) is:
> Though! the result that I get from mapscript is:
> I can't relize any systematic error.
This is a tough problem indeed! I have no clue.
Going from x, y = 552000, 4098077 through Transverse Mercator in the GGRS87
system should produce lat, lon = 37.027448, 24.584634 deg. A geocentric
shift as mentioned should produce lat, lon = 37.030039, 24.586333.
The ArcGIS values seem very unlikely; on the GRS80 globe they are nearly 21
kilometers away from the regular TM values. Datumshifting from GRS80 to
WGS84 cannot result in such large differences; the ellipsoids are nearly the
same and the cartesian shifts are less than 250 meters.
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