Hi David,<br><br>Can you clip out a small section of your DEM that contains both ocean and land and send it to me? Your question sounds interesting, and I'd like to take a look at the data before I comment on it.<br><br>
Thanks,<br><br>Roger<br>--<br><br><div class="gmail_quote">On Wed, Apr 7, 2010 at 9:08 PM, David <span dir="ltr"><<a href="mailto:dbainbridge@gmail.com">dbainbridge@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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:<br>
<br>
gdalwarp -of GTiff -co "TILED=YES" -dstalpha -srcnodata 0 -wt Float32 -ot Float32 -wo SAMPLE_STEPS=100 -multi N40W125.hgt test.tiff<br>
<br>
gdalinfo -mm gives:<br>
Band 1 Block=256x256 Type=Float32, ColorInterp=Gray<br>
Computed Min/Max=-32768.000,1233.000<br>
Band 2 Block=256x256 Type=Float32, ColorInterp=Alpha<br>
Computed Min/Max=0.000,255.000<br>
<br>
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.<br>
<br>
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.<br>
<br>
Is my approach a good idea and/or what am I missing to mask the ocean areas into the alpha layer?<br>
Thanks for any help.<br>
<br>
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</blockquote></div><br>