I've been trying to use GDAL to convert from an arbitrary projection/datum into Equirectangular (aka Plate Caree, aka Equidistant Cylindrical, aka Geographic, aka Lat/Long) with WGS84 datum. All of my input files have an associated PRJ file that I've been using with GDAL with this statement:
gdalwarp -s_srs Input.prj -t_srs Output.prj Input.xyz Output.tif
So far, I've had mixed results. I've been able to successfully transform a Lambert Equal Area projection in WGS84 to Geographic/WGS84, but performing a transform on LEA in RT90 projection causes an error of ~1km.
Stranger still, I tried to transform two Sinusoidal projections in RT90 and in WGS84, both of which resulted in an error of 16km! I suspect that these errors are largely due to some sort of ellipsoid/sphere discrepancy.
I'm very confused as to why these errors are so random, but more concerned that they are happening at all. Shouldn't
gdalwarp take any ellipsoid information about the source and target from the PRJ files and transform between them?
What can I do to correct my issue?