Cannot open a USGS DEM file?

[dmalav]

Hi,

I could not open this USGS DEM file using GDAL. I checked the file with other dem viewing programs and it looks fine there.

I am using the following code.

GDALAllRegister();

poDataset = (GDALDataset *) GDALOpen( DemFile?, GA_ReadOnly ); if( poDataset == NULL ) {

acad_printf("Error opening file %s\n%s\n",DemFile?, CPLGetLastErrorMsg()); CPLFreeConfig(); return 0;

}

It comes with an error "not recognised as a supported file format."

File is attached, if you do not see the file please let me know. Any help would be greatly appreciated. Thanks, Dinesh

[dmalav]

USGS DEM File

[warmerdam]

I have come to the conclusion that the file is non-standard in at least a couple ways.

• At byte 150 it uses code " 4" for the "code defining elevation pattern" field instead of the usual " 1".
• The first B record has a column number of 0 instead of 1.

I reviewed the latest version of the sdts2dem program used to generate the file, and I don't see how it could have produced the indicated elevation pattern value. So that's sort of weird. Perhaps because it was generated with an older version?

In any event, I have modified usgsdemdataset.cpp to ignore these two quirks and then reading seems to work fine. Changes are in trunk (r14380) and 1.5 (r14381).