[gdal-dev] KernelFilteredSource and nodata

[Chaitanya kumar CH]

Ken,

KernelFilteredSource is derived from SimpleSource. It does not support
setting a nodata value to the source band.
Make sure your source image has a nodata value. You can set it using
gdal_translate with the -a_nodata option.

On Fri, Nov 19, 2010 at 2:10 AM, Boss, Ken (DNR) <Ken.Boss at state.mn.us>wrote:

> Chaitanya--
>
> Thanks much for your response.
>
> I don't think that I described my problem effectively.  Let me restate it
> and see if we are talking about the same thing.
>
> Here is a .vrt file that I think should accomplish what I am after:
>
> <VRTDataset rasterYSize='690' rasterXSize='575'>
>  <SRS>EPSG:26915</SRS>
>  <GeoTransform>190000, 1000, 0, 4795000, 0, 1000</GeoTransform>
>  <VRTRasterBand band='1' dataType='Byte'>
>    <KernelFilteredSource>
>
>  <SourceFilename>D:/MyFiles/aptana_workspace/fire-webpage-mgmt/data/tmp_images/interpolated.tif</SourceFilename>
>       <SourceBand>1</SourceBand>
>      <NoDataValue>255</NoDataValue>
>       <Kernel normalized="1">
>        <Size>5</Size>
>        <Coefs>0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
> 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04</Coefs>
>      </Kernel>
>    </KernelFilteredSource>
>  </VRTRasterBand>
> </VRTDataset>
>
> I believe this file to be saying that interpolated.tif uses a value of 255
> for nodata, and that the kernel is to be normalized - that is, it should:
>
>  o ignore any nodata pixels within the kernel window when operating on a
> valid pixel
>  o adjust the coefficients to sum to one for the number of valid pixels in
> the window when operating on a valid pixel
>  o do nothing at all when centered on a nodata pixel
>
> I would expect then that any pixels that go in as nodata should come out as
> nodata, and that pixels with valid data values that are near nodata pixels
> should not be influenced by them.
>
> However, the outputs are not what I expect.  The averaging is applied to
> both nodata and valid pixels alike.  Have I set this up correctly, and is
> there a bug somewhere, or (more likely) is my vrt improperly constructed?
>
> Thanks for your help,
>
> --Ken
>
> > -----Original Message-----
> > From: Chaitanya kumar CH [mailto:chaitanya.ch at gmail.com]
> > Sent: Wednesday, November 17, 2010 11:11 PM
> > To: Boss, Ken (DNR)
> > Cc: gdal-dev at lists.osgeo.org
> > Subject: Re: [gdal-dev] KernelFilteredSource and nodata
> >
> > Ken,
> >
> > The current kernel filter does not ignore the boundaries of nodata
> pixels. But it
> > does normalize the kernel after ignoring the nodata pixels in the kernel,
> if the
> > 'normalized' attribute is set to 1.
> >
> > You can raise a ticket to request for this feature at
> > http://trac.osgeo.org/gdal/newticket
> >
> >> On Thu, Nov 18, 2010 at 6:08 AM, Boss, Ken (DNR) <Ken.Boss at state.mn.us>
> >> wrote:
> >> Hello list--
> >>
> >> I am attempting to filter a raster using gdal_translate (v 1.7) and a
> vrt with a
> >> KernelFilteredSource.  The input raster contains large areas of "nodata"
> values.  I
> >> would like the filter to ignore those areas.  I have tried various
> combinations of
> >> <NoDataValue>, <HideNoDataValue>, <NODATA> and <Kernel normalized='1'>,
> >> but have not been able to prevent the filter from applying itself at
> data/nodata
> >> boundaries.
> >>
> >> My current VRT and gdal_translate command lines are below.  Can anyone
> tell me
> >> what I am doing wrong?
> >>
> >> Thanks,
> >>
> >> Ken Boss
> >> Minnesota DNR
> >>
> >> ===== kernel_filter.vrt ===================
> >>
> >> <VRTDataset rasterYSize='690' rasterXSize='575'>
> >>  <SRS>EPSG:26915</SRS>
> >>  <GeoTransform>190000, 1000, 0, 4795000, 0, 1000</GeoTransform>
> >>  <VRTRasterBand band='1' dataType='Byte'>
> >>    <KernelFilteredSource>
> >>      <SourceFilename>interpolated.tif</SourceFilename>
> >>      <SourceBand>1</SourceBand>
> >>      <NoDataValue>255</NoDataValue>
> >>      <HideNoDataValue>1</HideNoDataValue>
> >>      <Kernel normalized='1'>
> >>        <Size>5</Size>
> >>        <Coefs>0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
> 0.04 0.04 0.04
> >> 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04</Coefs>
> >>      </Kernel>
> >>    </KernelFilteredSource>
> >>  </VRTRasterBand>
> >> </VRTDataset>
> >>
> >> =====================================
> >>
> >> gdal_translate -of GTiff -ot Byte -a_srs EPSG:26915 kernel_filter.vrt
> >> kernel_filtered.tif
> >>
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >
> >
> >
> > --
> > Best regards,
> > Chaitanya kumar CH.
> > /tʃaɪθənjə/ /kʊmɑr/
> > +91-9494447584
> > 17.2416N 80.1426E
>



-- 
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
17.2416N 80.1426E
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