when performing range doppler terrain correction (from GRD Data) with reprojection to a customized azimuthal equidistant projection (
+proj=aeqd +lat_0=53 +lon_0=24 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs) the resulting coordinates are off by about 400m from where they should be (eastward shift, latitude seems to be fine). No false easting is specified.
The proj4 string as displayed by gdal is correct and what I expected.
It doesn’t matter whether the output format is BEAM-DIMAP or GeoTiff.
The map projection is defined in the terrain correction module by selecting “Azimuthal Equidistant” (WGS84) and specifying the projection parameters: Latitude of origin = 53.0 and Central meridian= 24.0
Here’s an example graph: terraincorrect_aeqd.xml (3.7 KB)
And an example scene: S1A_IW_GRDH_1SDV_20141004T044317_20141004T044342_002675_002FBB_9677
When viewing the image in SNAP it looks fine relative to Sentinel 2 imagery for example.
However viewing it in any other GIS (QGIS; ENVI; GRASS) results in the wrong offset.
Also, if I run gdalwarp on it and reproject back to LatLong the offset remains.
Reprojecting to LatLong within SNAP results in a correctly projected image.
So either SNAP knows something GDAL or ENVI don’t (I couldn’t think of what that might be) or the transformation in SNAP is wrong (albeit consistently wrong, since the back transform to LatLong works fine)
Here’s what it looks like in QGIS (red tones are LatLong, and verified correct, blue tones are originally AEQD projected by SNAP and then reprojected to LatLong by gdalwarp):