Ssobieraj, If the 16 km offset is in N-S direction, and the E-W error is small, it might be a sphere/ellipsoid problem. From your RT90 I am guessing you're in Sweden, at which latitude you would expect approximately this error. The effect is beyond projection, latlong/sphere to latlong/WGS84 gives equally long offsets. Try using cs2cs and specify ellipsoids for both input and output.
There were some discussions on the gdal-dev list about this in June 2007. It is only when one of the ellipsoids is a sphere you get these large errors, otherwise the error resulting from messing up ellipsoids is much smaller. Hope this helps, Sjur K :-) -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of ssobieraj Sent: 1. desember 2010 17:52 To: [email protected] Subject: [gdal-dev] Re: Require Help Transforming into Equirectangular Hi Jean-Claude, Thanks for the help. To test the effect that I was getting, I created a total of four images. Two in Sinusoidal projection, using WGS84 and RT90, and another pair using Lambert Equal Area (again with both WGS84 and RT90 datum). I then compared these to an unaltered Equirectangular projected image in WGS84. The results seemed odd and so I've provided them below: The Sinusoidal projections were both 16km from my source, regardless of whether I used RT90 or WGS84. The Lambert projection using WGS84 transformed back perfectly. The Lambert projection using RT90 transformed back with a ~900m error, similar to what was seen when I used Vincent's method above. So it's possible that the +towgs84 parameters are at fault, but then why would the Sinusoidal/WGS84 be as bad as the Sinusoidal/RT90? -- View this message in context: http://osgeo-org.1803224.n2.nabble.com/Require-Help-Transforming-into-Equirectangular-tp5789691p5792571.html Sent from the GDAL - Dev mailing list archive at Nabble.com. _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
