Hello. I am having a terrible time trying to figure out how to convert what
should be value/height of 0 in the SRTM/hgt data file to the alpha layer in a
tiff. I was experimenting with making ocean areas transparent. I tried the
following with no success:
gdalwarp -of GTiff -co "TILED=YES" -dstalpha -srcnodata 0 -wt Float32 -ot
Float32 -wo SAMPLE_STEPS=100 -multi N40W125.hgt test.tiff
gdalinfo -mm gives:
Band 1 Block=256x256 Type=Float32, ColorInterp=Gray
Computed Min/Max=-32768.000,1233.000
Band 2 Block=256x256 Type=Float32, ColorInterp=Alpha
Computed Min/Max=0.000,255.000
Since this may affect the hillshading for any land areas inland I was also
going to attempt the same affect by masking the ocean after the hillshading.
The resulting tiff in either case would be overlaid onto another layer that
would have any land areas filled in with the resulting color that would have
been used with height 0 in the hgt file. I am doing this because I have a
coastline shapefile that represents land areas but not ocean areas.
Is my approach a good idea and/or what am I missing to mask the ocean areas
into the alpha layer?
Thanks for any help.
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