[gdal-dev] KernelFilteredSource and nodata
Chaitanya kumar CH
chaitanya.ch at gmail.com
Thu Nov 18 23:59:06 EST 2010
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:
> 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'>
> <GeoTransform>190000, 1000, 0, 4795000, 0, 1000</GeoTransform>
> <VRTRasterBand band='1' dataType='Byte'>
> <Kernel normalized="1">
> <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>
> 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,
> > -----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
> >> 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
Chaitanya kumar CH.
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