[gdal-dev] DEM format and what difference between dem and geotiff

[weixj2003ld]

1.I use GDAL to read a DEM file,and its extension is .img ,what other extensions for DEM file?
2.When I reand a geotff file and a dem file,I find that the dfference between them as follows:
                                                                                                              geotiff:             Dem
     GetDriver()->GetDescription() :                                                         GTiff,          HFA
     GetDriver()->GetMetadatItem(GDAL_DMD_LONGNAME):                GeoTIFF     Drdas Imagine Images(.img)
     bandnumber                                                                                           6                 1
 
Now,I want to know that,the bandnumber of DEM file is always 1?
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