[Gdal-dev] gdalwarp: different results with proj4 and WKT SRS information

[Nicolas Ribot]

Thanx for the insight, Joaquim.

Should I file a bug ?

On 12/6/06, Joaquim Luis <jluis at ualg.pt> wrote:
> Nicolas Ribot wrote:
> > Hi all,
> >
> > I noticed the following behaviour with gdalwarp:
> >
> > When warping an image, I set the t_srs parameter to be a PROJ4 string
> > coming from a MapInfo tab file (projection got with:
> >
> > ogr.Open(poly_filename).GetLayer(0).GetSpatialRef().ExportToProj4()
> > where poly_filename is the name of the TAB file
> >
> > The warped image is not correct and I can see a slight shift between
> > the image and the mapinfo TAB file displayed on it.
> >
> > When I do not use the proj4 string, but instead a file containing the
> > WKT srs definition got from the same TAB file, I get the correct
> > result for the warped image.
> >
> > Am I missing something with t_srs parameter ?
> >
> > Here is the proj4 string from my MAPINFO file:
> > +proj=lcc +lat_1=60 +lat_2=69 +lat_0=60 +lon_0=-132.5 +x_0=0 +y_0=0
> > +ellps=GRS80 +datum=NAD83 +units=m +no_defs
> >
> > and the WKT SRS from the same file:
> > PROJCS["unnamed",GEOGCS["unnamed",DATUM["North_American_Datum_1983",SPHEROID["GRS
> >
> > 80",6378137,298.257222101],TOWG
> > S84[0,0,0,-0,-0,-0,0]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Con
> >
> > ic_2SP"],PARAMETER["standard_parallel_1",60],PARAMETER["standard_parallel_2",69],PARAMETER["latitude_of_origin",6
> >
> > 0],PARAMETER["central_meridian",-132.5],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1
> >
> > .0]]
>
> Indeed there seams to exist a problem here.
> When I convert the proj4 string, I get a different WKT. Notice that the
> PROJECTION is different.
>
> PROJCS["unnamed",
>     GEOGCS["NAD83",
>         DATUM["North_American_Datum_1983",
>             SPHEROID["GRS 1980",6378137,298.257222101,
>                 AUTHORITY["EPSG","7019"]],
>             TOWGS84[0,0,0,0,0,0,0],
>             AUTHORITY["EPSG","6269"]],
>         PRIMEM["Greenwich",0,
>             AUTHORITY["EPSG","8901"]],
>         UNIT["degree",0.0174532925199433,
>             AUTHORITY["EPSG","9108"]],
>         AXIS["Lat",NORTH],
>         AXIS["Long",EAST],
>         AUTHORITY["EPSG","4269"]],
>     PROJECTION["Lambert_Conformal_Conic_1SP"],
>     PARAMETER["latitude_of_origin",60],
>     PARAMETER["central_meridian",-132.5],
>     PARAMETER["scale_factor",1],
>     PARAMETER["false_easting",0],
>     PARAMETER["false_northing",0],
>     UNIT["Meter",1]]
>
> Joaquim Luis
>
>
>