[Gdal-dev] spheroid to sphere (gdalwarp)

[Naiara Pinto]

Hi all,

I am trying to project some layers from Lat Long (WGS84 and NAD83)
into Lambert Azimuthal Equal Area (ellipse = Sphere). Here is the
command I use:

gdalwarp -s_srs '+proj=longlat +ellps=GRS80 +datum=NAD83 +no_defs'
-t_srs '+proj=laea +lat_0=44.807685 +lon_0=-100 +ellps=sphere +x_0=0
+y_0=0 +units=m +no_defs' -tr 30 30 -rn  -srcnodata -9999 -dstnodata
-9999 land_cover.tif pland_cover.tif

The center latitude of the output layer is actually 45N, but it seems
GDALWARP defines the latitude in accordance with the datum of the
source file.
I used this command with several layers and they all line up. The
problem is that they don't line up with the layer that was originally
in Lambert Azimuthal Equal Area. The projected layers seem to be
shifted east (although the fit looks better in the center).

Is there a problem transforming the data from spheroid to sphere, and
if so, what could I do to get around this?

Thanks!

Naiara.