[gdal-dev] Re: Require Help Transforming into Equirectangular

[ssobieraj]

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?


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