Nikos Alexandris wrote:
Markus,
I appreciate it that you clarify the details.
It seems I try but fail. Something is still wrong...
If you remove the associated
colour table, r.out.gdal writes a completely black colour table.
Applications that read the colour table will consequently show a
completely black image, but the true values are still there. I think
this is a bug in r.out.gdal.
If there is no colour table, no colour
table should be written to the output file at all, because only then
would other applications use the real values to display the image. Fixed
after removing lines 208 and 210 in raster/r.out.gdal/main.c and
compiling again, GRASS 6.3.0
The lines read:
line 208
hCT = GDALCreateColorTable(GPI_RGB);
line 210
GDALSetRasterColorTable(hBand, hCT);
Did you already filed a ticket for that?
Not yet, will do.
So nodata=255 does not mean "loss of information"?
The red, green, blue channels are 8-bit (2 high 8 = 256, values counting
from 0 up to 255).
It means that NULL cells in the GRASS raster are replaced with 255 or
the specified nodata value.
One example report for an image imported with r.in.gdal, MASKed,
r.colors -r, r.out.gdal as a group with nodata=-9999:
Driver: GTiff/GeoTIFF
Files: simmern_2624_5548.tiff
simmern_2624_5548.tiff.aux.xml
Size is 2500, 2500
Coordinate System is:
PROJCS["Transverse Mercator",
GEOGCS["bessel",
DATUM["Deutsches_Hauptdreiecksnetz",
SPHEROID["Bessel 1841",6377397.155,299.1528128000008,
AUTHORITY["EPSG","7004"]],
AUTHORITY["EPSG","6314"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433]],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",0],
PARAMETER["central_meridian",6],
PARAMETER["scale_factor",1],
PARAMETER["false_easting",2500000],
PARAMETER["false_northing",0],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]]]
Origin = (2624000.000000000000000,5550000.000000000000000)
Pixel Size = (0.800000000000000,-0.800000000000000)
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left ( 2624000.000, 5550000.000) ( 7d43'56.88"E, 50d 4'28.10"N)
Lower Left ( 2624000.000, 5548000.000) ( 7d43'54.54"E, 50d 3'23.39"N)
Upper Right ( 2626000.000, 5550000.000) ( 7d45'37.42"E, 50d 4'26.59"N)
Lower Right ( 2626000.000, 5548000.000) ( 7d45'35.05"E, 50d 3'21.88"N)
Center ( 2625000.000, 5549000.000) ( 7d44'45.97"E, 50d 3'54.99"N)
Band 1 Block=2500x1 Type=Byte, ColorInterp=Red
NoData Value=-9999
Metadata:
COLOR_TABLE_RULES_COUNT=5
COLOR_TABLE_RULE_RGB_0=0.000000e+00 4.640000e+01 255 255 0 0 255 0
COLOR_TABLE_RULE_RGB_1=4.640000e+01 9.280000e+01 0 255 0 0 255 255
COLOR_TABLE_RULE_RGB_2=9.280000e+01 1.392000e+02 0 255 255 0 0 255
COLOR_TABLE_RULE_RGB_3=1.392000e+02 1.856000e+02 0 0 255 255 0 255
COLOR_TABLE_RULE_RGB_4=1.856000e+02 2.320000e+02 255 0 255 255 0 0
Band 2 Block=2500x1 Type=Byte, ColorInterp=Green
NoData Value=-9999
Metadata:
COLOR_TABLE_RULES_COUNT=5
COLOR_TABLE_RULE_RGB_0=0.000000e+00 4.680000e+01 255 255 0 0 255 0
COLOR_TABLE_RULE_RGB_1=4.680000e+01 9.360000e+01 0 255 0 0 255 255
COLOR_TABLE_RULE_RGB_2=9.360000e+01 1.404000e+02 0 255 255 0 0 255
COLOR_TABLE_RULE_RGB_3=1.404000e+02 1.872000e+02 0 0 255 255 0 255
COLOR_TABLE_RULE_RGB_4=1.872000e+02 2.340000e+02 255 0 255 255 0 0
Band 3 Block=2500x1 Type=Byte, ColorInterp=Blue
NoData Value=-9999
Metadata:
COLOR_TABLE_RULES_COUNT=5
COLOR_TABLE_RULE_RGB_0=3.400000e+01 7.320000e+01 255 255 0 0 255 0
COLOR_TABLE_RULE_RGB_1=7.320000e+01 1.124000e+02 0 255 0 0 255 255
COLOR_TABLE_RULE_RGB_2=1.124000e+02 1.516000e+02 0 255 255 0 0 255
COLOR_TABLE_RULE_RGB_3=1.516000e+02 1.908000e+02 0 0 255 255 0 255
COLOR_TABLE_RULE_RGB_4=1.908000e+02 2.300000e+02 255 0 255 255 0 0
I have one last idea. Type is Byte, but NoData Value=-9999, out of range
for Byte. Maybe that causes a problem? Can you try with nodata=0, then
NULL cells in the GRASS raster should appear black in the GeoTIFF?
If that fails too, maybe it's the COLOR_TABLE_RULE entries. Then try
data type = INT16, not UINT16, after removing the colour table with
r.colors -r, this should remove both any colour table and these colour
table rule entries in the GeoTIFF metadata.
Good luck!
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