[Gdal-dev] gdalwarp reprojection shift

[Matthew Perry]

Wim,

On 8/16/06, chalmet at telusplanet.net <chalmet at telusplanet.net> wrote:
> If I do this using gdalwarp, I have a shift of about 70 meters compared to my
> reprojected tiles in PCI and ERmapper. I use the following command for gdalwarp:
>
> *******************
> gdalwarp -s_srs "+proj=tmerc +datum=NAD83 +x_0=500000 +lon_0=-115 +lat_0=0
> +k=0.9992" -t_srs "+proj=latlong +datum=NAD27" -rc -tr 0.000035 0.000035
> 400113.tif 400113_latlong.tif
> *******************
>
> Does anybody know why this is happening. And more importantly, how could I make
> the gdalwarp tiff line up with my other tiffs, meaning avoid the 70m shift?


Most likely your version of proj4 (which gdal uses for reprojecting
coordinates) is not built with support for datum shifts. The proj4 faq
is pretty helpful for this issue...
http://proj.maptools.org/faq.html.

You might have to rebuild proj4 with the datum support files or you
can download FWTools (for win and linux) that has proj4 precompiled
with the datum shift files.
-- 
Matt Perry
perrygeo at gmail.com
http://www.perrygeo.net