I've downloaded the .DEM files from the NASA SRTM30 dataset (found here) however trying to open these yields
ERROR 4: "E140N90.DEM" is not recognized as a supported file format.
This is the the same while either using the windows binaries with python bindings and OSGeo4W shell. OSGeo is using GDAL 2.2.2 and USGSDEM files are listed under the supported formats in
... USGSDEM -raster- (rwv): USGS Optional ASCII DEM (and CDED) ...
I've also tried opening the files in QGis, which has yielded the same result. So is there another way to open the files, or convert the files into a supported file format?