I sent an other reply today this morning though it has not appeared yet, so I suppose I must rewrite it and resend it. So...
Let's take a more standard tranformation and let's (together) evaluate the results. I will use as my starting coordinate system the standard greek grid system (GGRS87). As found on the web page http://cvs.gis.umn.edu/cgi-bin/viewcvs/mapserver_docs/proj.html?rev=1.2#GGRS87%20/%20Greek%20Grid the parameters of this system are: proj=tmerc lat_0=0.000000000 lon_0=24.000000000 k=0.999600 x_0=500000.000 y_0=0.000 ellps=GRS80 towgs84=-199.87,74.79,246.62,0,0,0,0 units=m no_defs Here, I will inform that the greek system has its borders on Xmin = 80000 Xmax = 1050000 Ymin = 3760000 Ymax = 4660000 Supposing that these params are official and accepted enough, I step over to the tranformation from this system (GGRS87) to WGS84. So we have the following code: [CODE] // Projections declaration $projInObj=ms_newprojectionobj("proj=tmerc,ellps=GRS80,towgs84=-199.87,74.79 ,246.62,0,0,0,0,units=m,lon_0=24,k=0.9996,x_0=500000,no_defs") $projOutObj=ms_newprojectionobj("proj=latlong,ellps=WGS84,DATUM=WGS84,no_defs"); // Shape to be reprojected $myshape = ms_newpointobj(); $myshape->setXY(552000, 4098077); // Some code to confirm initial values print_r($myshape); echo "<p />"; $myshape->project($projInObj, $projOutObj); // Code to get the final values print_r($myshape); [/CODE] The expected result (according to very reliable software like ArcGIS and others...) is: lon=24,351076881,lat=37,014812887 Though! the result that I get from mapscript is: lon=24.585568772,lat=37.028433901 Again it seems to a small difference but the truth is that we have to deal with a very large difference on the results! I did test the tranformation with different values. I provide some triads of input and output: <triad 1> Input: X=100000, Y=4000000 Expected: lon:19,334046546,lat:36,035407643 mapscript gave: lon:19.560466687 lat:36.063361179 </triad 1> <triad 2> Input: X=400000, Y=4200000 Expected: lon:22,514890564,lat:37,564089629 mapscript gave: lon:22.862809496,lat:37.943105553 </triad 2> <triad 3> Input: X=700000, Y=4400000 Expected: lon:26,200754084,lat:39,434436875 mapscript gave: lon:26.334654875,lat:39.727476986 </triad 3> <triad 4> Input: X=1000000, Y=4600000 Expected: lon:29,585420281,lat:41,235432698 mapscript gave: lon:29.980956617,lat:41.396983529 </triad 4> I can't relize any sytematic error. The only thing that can mention by a first look is that I get bad results. And, once again, I ask: Do I do something wrong or are there any limitations on the PROJ or the mapscript that I must know? Thanks on advance Andreas Trantidis
