Hi all,
This is a similar question to that posed in
<https://lists.osgeo.org/pipermail/gdal-dev/2011-November/030880.html>,
which didn't seem to be resolved on the mailing list.
Basically, I am running the following command:
gdaldem color-relief dhaka.tif colour-relief.ramp
dhaka-colour-relief.tif -alpha -of GTiff -co COMPRESS=DEFLATE -co
PREDICTOR=1 -co ZLEVEL=9 -co TILED=YES
colour-relief.ramp is as follows:
500 0 1 36
300 12 15 118
75 33 109 158
30 63 184 105
3 120 234 50
0 254 255 125
nv 0 0 0 0
dhaka.tif is as follows:
Driver: GTiff/GeoTIFF
Files: dhaka.tif
Size is 443, 217
Coordinate System is:
GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433],
AUTHORITY["EPSG","4326"]]
Origin = (90.314286342329481,23.848152313769823)
Pixel Size = (0.000833292764088,-0.000833299630454)
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
COMPRESSION=DEFLATE
INTERLEAVE=BAND
Corner Coordinates:
Upper Left ( 90.3142863, 23.8481523) ( 90d18'51.43"E, 23d50'53.35"N)
Lower Left ( 90.3142863, 23.6673263) ( 90d18'51.43"E, 23d40' 2.37"N)
Upper Right ( 90.6834350, 23.8481523) ( 90d41' 0.37"E, 23d50'53.35"N)
Lower Right ( 90.6834350, 23.6673263) ( 90d41' 0.37"E, 23d40' 2.37"N)
Center ( 90.4988607, 23.7577393) ( 90d29'55.90"E, 23d45'27.86"N)
Band 1 Block=256x256 Type=Float32, ColorInterp=Gray
NoData Value=nan
All files are available at <http://dropcanvas.com/yazx9>.
I find that the NODATA values are assigned the maximum colour value in
dhaka-colour-relief.tif i.e. RGBA 0 1 36 255.
Changing the NODATA to -1 using `gdal_translate -a_nodata -1` does not
seem to affect this outcome. I have tested this using both GDAL 1.11.2
and a recent trunk build on Linux.
Does anyone have any ideas on making the nodata value transparent in the
colour relief output?
Many thanks,
Homme.
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