raster - Why does GDAL open a DTED file as a vector format?

GDAL version: 2.1.1

Language: C++

Given the path of a geospatial file, I want to know whether the file is a raster or vector format. The only way I have found so far to make that distinction is to attempt to open the file as vector format first. If that succeeds, then treat it as a vector file; otherwise, attempt to open the file as raster format. The following code snippet is an example.

This worked for GeoTIFF and shape files.

However, for a DTED file, opening it with the GDAL_OF_VECTOR flag gives me a valid dataset handle. So, my code incorrectly decides that it is a vector format.

Why did GDALOpenEx() open the DTED file when the GDAL_OF_VECTOR flag was used?

void test( string const & path )
{

  GDALDatasetH hDataset;
  bool isRaster = false;

  unsigned int openFlags = GA_ReadOnly | GDAL_OF_VECTOR;
  hDataset = GDALOpenEx( path.c_str(), openFlags, NULL, NULL, NULL );
  if ( hDataset )
  {
    printf( "Opened as vector\n" );
    isRaster = false;
  }

  else
  {
    openFlags = GA_ReadOnly;
    hDataset = GDALOpenEx( path.c_str(), openFlags, NULL, NULL, NULL );
    if ( hDataset )
    {
      printf( "Opened as raster\n" );
      isRaster = true;
    }
    else

    {
      printf( "Not opened, skip it\n" );
      return;
    }
  }

  // Process the file differently, depending on its format.
  if ( isRaster )
  {
    ...

  }
  else
  {
    ...
  }

  GDALClose( hDataset );
}

Answer

You can use GetRasterCount() to test if the dataset is raster and GetLayerCount() for vector.

http://osgeo-org.1560.x6.nabble.com/Discover-whether-a-GDALDataset-is-raster-or-vector-td5270223.html

For future reference, GDAL_OF_VECTOR does mean what you thought it meant, i.e only try vector drivers. However when you attempted to open the DTED file with the GDAL_OF_VECTOR flag, the SEG-Y driver opens it "successfully". I think it's a bug in the SEG-Y driver.

For example (in python):

from osgeo import gdal
print(gdal.__version__)

f = "n43.dt0"
ds = gdal.OpenEx(f, gdal.OF_VECTOR)

drv = ds.GetDriver()

print(drv.GetMetadata())

Output:

2.1.3
{'DCAP_OPEN': 'YES', 
 'DCAP_VECTOR': 'YES', 
 'DCAP_VIRTUALIO': 'YES', 
 'DMD_HELPTOPIC': 'drv_segy.html', 
 'DMD_LONGNAME': 'SEG-Y'}