[gdal-dev] gdalwarp and geogrids

[Wood, Alexander]

Hello,

Hello devlist,
I have small patch of alaska elevation data  in utm4/navd88 and I would like to convert this into wgs84 ellipsoidal.  I know this data uses navd88,but gdalinfo does not report this vertical datum in the WKT.  To reproject this data into wgs84 ellipsoidal elevation, I'm assuming it should be possible with the following gdalwarp command:

gdalwarp -s_srs "+proj=utm +zone=4 +datum=WGS84 +units=m +no_defs +geoidgrids=g2009alaska.gtx" -t_srs "+proj=longlat +datum=WGS84 +units=m +no_def" alaska_sample_utm4_navd88.tif alaska_sample_wgs84.tif

I'm seeing the following errors reported from this command:
ERROR 1: point not within available datum shift grids
ERROR 1: GDALWarperOperation::ComputeSourceWindow() failed because the pfnTransformer failed.
Warning 1: Unable to compute source region for output window 0,0,351,106, skipping.

I'm using the geoidgrids from http://trac.osgeo.org/proj/wiki/VerticalDatums, moved into the gdal/projlib directory

The source file is in utm4:
PROJ.4 string is:
'+proj=utm +zone=4 +datum=WGS84 +units=m +no_defs '
Origin = (412011.848695503660000,7085064.815277445100000)

For reference, this is about 100msurrounding the following lat/long:
Center      (-160.7909106,  63.8815138) (160d47'27.28"W, 63d52'53.45"N)

A simple gdalinfo on g2009alaska.gtx reports the following:
PROJ.4 string is:
'+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs '
Origin = (171.991666666666670,72.008333333333340)
Pixel Size = (0.016666666666667,-0.016666666666667)
Corner Coordinates:
Upper Left  ( 171.9916667,  72.0083333) (171d59'30.00"E, 72d 0'30.00"N)
Lower Left  ( 171.9916667,  48.9916667) (171d59'30.00"E, 48d59'30.00"N)
Upper Right (     234.008,      72.008) (234d 0'30.00"E, 72d 0'30.00"N)
Lower Right (     234.008,      48.992) (234d 0'30.00"E, 48d59'30.00"N)
Center      (     203.000,      60.500) (203d 0' 0.00"E, 60d30' 0.00"N)

Does anyone see anything wrong with my gdalwarp/proj4 usage?  Are there better ways to handle these sorts of transformations?

Thanks,
Alex
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