[Gdal-dev] gdalwarp + nosrcdata

[Frank Warmerdam]

Robert Osfield wrote:
> Hi,
> 
> I have been using the GDAL Warp API successful for a while without filtering 
> out no source data.  I now am using a dataset that I'd like to manage the no 
> source data, and the API appears to support this, but as yet I haven't been 
> able to get it to work.  I'm setting up both the padfSrcNoDataReal/Imag and 
> padfDstNoDataReal/Img, but none of these settings appear to make any 
> difference to the final resultant image.  
> 
> I haven't found anything in the docs or warp tutorial to clarify all the 
> details, but looking at the gdalwap app source it looks like my 
> implementation shouldn't be too far off the mark. 
> 
> I have tried out the gdalwap app as well, and still see the same problem with 
> no source data making its way into the final warp image.
> 
> I'm not sure what to expect from gdalwarp, so a few pointers of what to expect 
> to be able to do, and how to go about it would be great.  I've pasted details 
> on what I've tried just in case this helps pinpoint the what steps I'm 
> missing.

Robert,

It looks like you are on the right track. I am not sure why it isn't working.

I tried the command "gdalwarp -srcnodata -32768 nzdem500 out.tif" to warp
a dem in ESRI Grid format to a tiff file, and it correctly ignore the -32768
values leaving the default value of 0 in the output file.

Is it possible you are working with an older version of the Warp API?

I think the comparisons are being done as floating point, so I am a bit
concerned that there may be floating point roundoff issues representing some
values properly.  I don't know if that is what might be happening here.

So, first verify you are using current code.  (1.2.0a/b or a recently
nightly snapshot) If it still doesn't work with a commandline form like the
above, then send me the DEM privately and I will see if I can reproduce the
problem.

Best regards,
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