[Gdal-dev] Creating an empty ColorTable in C++

[Frank Warmerdam]

Roger Bivand wrote:
  > My plan was to pass from R to GDAL the handles to two data sets, the
> output one of which would get populated by the color index band and the 
> color table. I now see a clean error exit:
> 
> Error in rgdal:::SGDF2RGB(xx) : 
>         GDAL Error 6: SetColorTable() not supported for existing TIFF files.
> 
> which suggests that I should rather initiate the output dataset in my 
> C/C++ code.

Roger,

I think the key here is that the GeoTIFF driver in GDAL only allows you
to assign a pseudocolor table to a file before you start any raster data.

>> I suspect that the GetColorTable() is returning NULL which is causing the
>> crash later on.
>>
>> Also, I notice you were using the C++ method to fetch the color table.
>> It is up to you, but if you were to use only the C API in an R interface
>> to GDAL it would make things much less "version fragile".  That is, new
>> versions of GDAL could be substituted without necessarily having to
>> recompile the R wrappers as the C API is much more ABI stable than the
>> C++ API.
>>
> 
> I'm very much building on and maintaining Tim Keitt's elegant C++ code, 
> which is written C++ style; as is evident C++ is not a language I enjoy, 
> but I would not want to have to rewrite Tim's earlier work. So the code 
> has stayed a mixture of elegance where I haven't done anything and 
> muddling through where I have written things.

OK, I can understand the desire to not rewrite everything.  I just wanted
to raise the issue.

Best regards,
-- 
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