[gdal-dev] help for including category names

[Even Rouault]

Marcel,

I guess that category name is a rarely used features by GDAL users and it 
wasn't actually supported by the custom CreateCopy() implementation of the 
GTiff driver.

I've just pushed into svn trunk (r22120) a fix so that 
GTiffDataset::CreateCopy() copies the category names from the source dataset. 
But note that the geotiff/tiff format makes no provision for category names, so 
the effect of this is to copy the data in a .aux.xml file next to the geotiff 
file. The .aux.xml file is a GDAL specific format.

In the meantime, you can generate the .aux.xml file by yourself. For example :

<PAMDataset>
  <PAMRasterBand band="1">
    <CategoryNames>
      <Category>Not processed</Category>
      <Category>Cloud-free land</Category>
    </CategoryNames>
  </PAMRasterBand>
</PAMDataset>

GDAL 1.8.0 will be able to fetch the category names from it.

Another possibility to avoid the .aux.xml file would be to extend the 
capabilities of the GDAL's specific TIFFTAG_GDAL_METADATA. Currently it only 
holds dataset and rasterband level metadata, but not category names. But such 
a change would be a bit more involved. Another issue to take into account is 
that maximum size of the content that can be written in the tag is limited to 
32000 bytes.

Best regards,

Even


Le mardi 05 avril 2011 16:05:04, Marcel Derrien a écrit :
> Hello,
> I am new with gdal, and it is my first post here.
> I have a gdal 1.8.0 installed on a cenOS Linux x86_64 ,with libtiff
> 3.9.4 and libgeotiff 1.3.0.
> I try the translation of a raster dataset to geotiff through a
> VRTRawRasterBand described in a VRT file using gdal_translate.
> gdal_translate test.vrt test.tif
> The VRT file includes a category list description that I would like to
> get in the resulting geotiff.
> The geotiff produced is correct but the only thing that is missing is
> the category names that I can't see with gdalinfo.
> It seems as if the category list was not managed, as the resulting file
> size is the same with and without the categorynames section in the VRT.
> I suspect my gdal installation or maybe I have a bad understanding of
> the way to manage this option.
> Could somebody help to find an explanation ?
> 
> gdal-config --version
> 1.8.0
> gdal-config --dep-libs
> -lsqlite3 -L/usr/lib64/lib -lexpat -lgif -ljpeg
> -L/export/util/libgeotiff-1.3.0/lib -lgeotiff
> -L/export/util/tiff-3.9.4/lib -ltiff -lpng -L/export/util/netcdf-3.6.2
> -L/export/util/netcdf-3.6.2/lib -lnetcdf -lz -lpthread -lm -lrt -ldl
> -L/usr/kerberos/lib64 -lcurl -lgssapi_krb5 -lkrb5 -lk5crypto -lcom_err
> -lresolv -ldl -lidn -lssl -lcrypto -lz
> 
> 
> gdalinfo t.tif
> 
> Driver: GTiff/GeoTIFF
> Files: t.tif
> Size is 3712, 3712
> Coordinate System is:
> PROJCS["Geostationary_Satellite",
>     GEOGCS["GCS_unnamed ellipse",
>         DATUM["D_unknown",
>             SPHEROID["Unknown",6378169,295.4880658970008]],
>         PRIMEM["Greenwich",0],
>         UNIT["Degree",0.017453292519943295]],
>     PROJECTION["Geostationary_Satellite"],
>     PARAMETER["central_meridian",0],
>     PARAMETER["satellite_height",35785831],
>     PARAMETER["false_easting",0],
>     PARAMETER["false_northing",0],
>     UNIT["Meter",1]]
> Origin = (-5570248.832537000067532,5570248.832537000067532)
> Pixel Size = (3000.403357000000142,-3000.403357000000142)
> Metadata:
>   AREA_OR_POINT=Area
> Image Structure Metadata:
>   INTERLEAVE=BAND
> Corner Coordinates:
> Upper Left  (-5570248.833, 5570248.833)
> Lower Left  (-5570248.833,-5567248.429)
> Upper Right ( 5567248.429, 5570248.833)
> Lower Right ( 5567248.429,-5567248.429)
> Center      (   -1500.202,    1500.202)
> Band 1 Block=3712x2 Type=Byte, ColorInterp=Palette
>   Color Table (RGB with 256 entries)
>     0: 100,100,100,255
> ....
> 
> Here is the VRT file content:
> <VRTDataset rasterXSize="3712" rasterYSize="3712">
>     <GeoTransform>-5570248.832537, 3000.403357, 0.000000,
> 5570248.832537, 0.000000, -3000.403357</GeoTransform>
> 
> <SRS>PROJCS[&quot;Geostationary_Satellite&quot;,GEOGCS[&quot;GCS_unnamed
> ellipse&quot;,DATUM[&quot;D_unknown&quot;,SPHEROID[&quot;Unknown&quot;,6378
> 169,295.4880658970008]],PRIMEM[&quot;Greenwich&quot;,0],UNIT[&quot;degree&q
> uot;,0.0174532925199433]],PROJECTION[&quot;Geostationary_Satellite&quot;],P
> ARAMETER[&quot;central_meridian&quot;,0],PARAMETER[&quot;satellite_height&q
> uot;,35785831],PARAMETER[&quot;false_easting&quot;,0],PARAMETER[&quot;false
> _northing&quot;,0],UNIT[&quot;metre&quot;,1]]</SRS> <Metadata>
>     <MDI key="AREA_OR_POINT">Area</MDI>
>     </Metadata>
>     <Description>Cloud Type Layer</Description>
>     <VRTRasterBand dataType="Byte" band="1" subClass="VRTRawRasterBand">
>         <ColorInterp>Palette</ColorInterp>
>             <ColorTable>
>                 <Entry c1="100" c2="100" c3="100"/>
>                 <Entry ...
>                 ...
>             </ColorTable>
>         <CategoryNames>
>             <Category>Not processed</Category>
>             <Category>Cloud-free land</Category>
>              ...
>             </CategoryNames>
>         <SourceFilename relativetoVRT="1">t.fis</SourceFilename>
>         <ImageOffset>7424</ImageOffset>
>         <PixelOffset>1</PixelOffset>
>         <LineOffset>3712</LineOffset>
>         <ByteOrder>LSB</ByteOrder>
>     </VRTRasterBand>
> </VRTDataset>
> 
> 
> 
> Thanks in advance,
> ---
> Marcel Derrien