[gdal-dev] VRT KernelFilteredSource and NoDataValue

Even Rouault even.rouault at mines-paris.org
Sun Aug 30 04:12:04 EDT 2009

Selon Belaid MOA <belaid_moa at hotmail.com>:


First, the VRTKernelFilteredSource will only recognize the nodata value if you
set it on the VRTRasterBand (it will not fetch it directly from the

When a nodata value is set and found in one of the values in a NxN square, the
value will be ignored. The effect of this depends whether normalized="1" is set
on <Kernel> or not. If normalized=1, the sum of the coefficients is not
incremented for that nodata value, so the normalization will operate only on
valid pixel values. If normalized=0, the nodata value is just ignored

As far as what happens in the borders is concerned, the code says that : "Fill
in missing areas.  Note that we replicate the edge valid values out.  We don't
using "mirroring" which might be more suitable for some times of filters.  We
also don't mark these pixels as "nodata" though perhaps we should."

Best regards,


> Hi everyone,
>     I am using VRT KernelFilteredSource to implement an average filter as
> done in the VRT tutorial. However, I am still unclear on how it handles the
> NoDataValue pixels. Are they too averaged or does it leave them as they are?
> If they are masked,  does do an adjustment for the kernel coefficients to
> compensate for their absence? Another related question, is how does it handle
> the pixels on the borders and the kernel coefficients for those pixels?
>    Thank you very very much in advance for any help on these issues.
>    With best regards.
> ~Belaid.
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