[Gdal-dev] Python USGS ASCII DEM

Norman Vine nhv at cape.com
Mon Jul 26 15:15:27 EDT 2004

Norman Barker writes:
> I am having problems with a bottleneck with the USGS ASCII DEMs that we 
> are using.  I understand from
> http://www.remotesensing.org/gdal/frmt_usgsdem.html that they are 
> treated as one tile and are thus loaded in
> completely.
> The line we are using is
>         dem_src_data = dem_band.ReadAsArray(0, (start_row + iY) , 
> src_tif.RasterXSize, 1)
> so we are trying to read a section as long as the input tif file from 
> the DEM.  The DEMS are over 100mb.
> All the other code is very fast thanks to GDAL, but is there a work 
> around for this bottle neck?

I reccomend translating all of your DEMS to 16bit greyscale geotiffs
ahead of time off line



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