[gdal-dev] Overviews are not taken into account while reading with specified resampling method

[Denis Rykov]

In GDAL 3.1 (previous example was done in GDAL 2.2.3) I can read data from
that VRT using "gdalconst.GRIORA_Cubic" but still overviews are not used:

>>> from osgeo import gdal
>>> from osgeo.gdal import gdalconst
>>> gdal.__version__
'3.1.0'
>>> url = "/vsicurl/https://gist.githubusercontent.com/drnextgis/3cbdbace7b5b8b80c3c6169b109bf9db/raw/7b61af41c698930a7f2da851a0684a15ddeb99a9/rasterio-boundless.vrt"
>>> ds = gdal.OpenEx(url)
>>> image = ds.ReadAsArray(xoff=0, yoff=0, xsize=64, ysize=64, buf_xsize=10, buf_ysize=10, resample_alg=gdalconst.GRIORA_Cubic)
>>> image.shape
(3, 10, 10)


On Thu, Aug 27, 2020 at 7:30 PM Denis Rykov <rykovd at gmail.com> wrote:

> Hi Sean. I patched rasterio as you suggested and intermediate file now
> looks like this (I'm trying now with a public dataset):
> https://gist.github.com/drnextgis/3cbdbace7b5b8b80c3c6169b109bf9db
>
> But when I read it with GDAL using non-nearest algorithm I'm getting
> the following error:
>
> >>> from osgeo import gdal>>> from osgeo.gdal import gdalconst>>> url = "/tmp/rasterio-boundless.vrt">>> ds = gdal.OpenEx(url)>>> image = ds.ReadAsArray(xoff=0, yoff=0, xsize=64, ysize=64, buf_xsize=10, buf_ysize=10, resample_alg=gdalconst.GRIORA_Cubic)
> ERROR 4: /tmp/dummy.tif: No such file or directory
>
> but with NearestNeighbour it works without error:
>
> >>> from osgeo import gdal>>> from osgeo.gdal import gdalconst>>> url = "/tmp/rasterio-boundless.vrt">>> ds = gdal.OpenEx(url)>>> image = ds.ReadAsArray(xoff=0, yoff=0, xsize=64, ysize=64, buf_xsize=10, buf_ysize=10, resample_alg=gdalconst.GRIORA_NearestNeighbour)>>> image.shape(3, 10, 10)
>
> I would be very appreciated if Even could explain why GDAL behaves
> differently depending on resample_alg.
>
> On Thu, Aug 27, 2020 at 6:39 PM Sean Gillies <sean at mapbox.com> wrote:
>
>> Hi Denis, Even,
>>
>> On Thu, Aug 27, 2020 at 8:08 AM Even Rouault <even.rouault at spatialys.com>
>> wrote:
>>
>>> On jeudi 27 août 2020 15:08:02 CEST Denis Rykov wrote:
>>>
>>> > I found the culprit. If remove this section from each band definition
>>> in
>>>
>>> > VRT file then everything works fine:
>>>
>>> >
>>>
>>> > <ComplexSource>
>>>
>>> > <SourceFilename relativeToVRT="1" shared="0">dummy.tif</SourceFilename>
>>>
>>> > <SourceBand>3</SourceBand>
>>>
>>> > <SourceProperties BlockXSize="128" BlockYSize="128"
>>>
>>> > RasterXSize="40961" RasterYSize="139265" dataType="Byte" />
>>>
>>> > <SrcRect xOff="0" xSize="1" yOff="0" ySize="1" />
>>>
>>> > <DstRect xOff="0" xSize="1" yOff="0" ySize="1" />
>>>
>>> > <ScaleRatio>0</ScaleRatio>
>>>
>>> > <ScaleOffset>0.0</ScaleOffset></ComplexSource
>>>
>>>
>>>
>>> I'm perhaps missing something, but the above snippet added by RasterIO
>>> doesn't make sense to me. It just sets the pixel at (0,0) to 0. I bet it is
>>> completely useless. It would make more sense to have xSize/ySize of DstRect
>>> to cover the whole raster. And as <NoDataValue> is set on the
>>> VRTRasterBand, this should be used to fill the target raster anyway.
>>>
>>>
>>>
>>> As far as why overviews of the original VRT aren't used is concerned,
>>> I'm not sure why. I'd have expected it to work, but I must be missing
>>> something.
>>>
>>>
>>>
>>> Even
>>>
>>
>> That's a rasterio bug: the background "dummy.tif" source should
>> be <DstRect xOff="0" xSize="40961" yOff="0" ySize="139265" />. I'm working
>> on a patch for this.
>>
>> This VRT background fill is different from nodata. The scale offset could
>> be different from the nodata value. BTW, It takes advantage of GDAL
>> shortcuts predicated on scale ratio. The "dummy.tif" file is never opened
>> and doesn't even exist.
>>
>> --
>> Sean Gillies
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>
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