[gdal-dev] GDALWarp on a specific overview of a dataset

[Thomas Sevaldrud]

Ah, great! That fixed it :-)

Is there an official 1.11.3 release in the works? It's a bit of hassle for
me to integrate it into our build system here, so if there's a new official
version out soon I probably won't bother to integrate the current snapshot.

Thanks so much for your help, Even!

- Thomas

On Mon, Jun 15, 2015 at 4:06 PM, Even Rouault <even.rouault at spatialys.com>
wrote:

> Le lundi 15 juin 2015 15:51:37, Thomas Sevaldrud a écrit :
> > When using the same image in GeoTIFF with overviews, it works correctly,
> > which may indicate something with the ECW drivers. I suppose it must be
> > something triggered by something weird I'm doing though, or else I would
> > think that other people would have the same problem.
>
> It is sometimes surprising that some bugs remain unreported for long!
>
> >
> > The weird thing is that if I simply add an extra band to the VRT it works
> > with ECW as well... This extra band is never used for anything and has no
> > source, but with it, I get the correct image.
>
> Interesting. My guess is that you must hit
> https://trac.osgeo.org/gdal/ticket/5954
>
> >
> > I can't switch to GDAL 2.0 yet, but I'll try to isolate the code from the
> > GDALOverviewDataset class and use that instead of the VRT approach, and
> see
> > if that makes any difference.
>
> Latest code from 1.11 branch has the fix for the above ticket.
>
> >
> > - Thomas
> >
> >
> > On Mon, Jun 15, 2015 at 12:19 PM, Even Rouault <
> even.rouault at spatialys.com>
> >
> > wrote:
> > > Thomas,
> > >
> > > 2 suggestions to help narrowing down the issue :
> > > - try gdalwarp of GDAL 2.0 that can select the most appropriate
> overview
> > > given the target resolution / raster size
> > > - try with the ECW translated as a GeoTIFF to check if it isn't an
> issue
> > > with
> > > the ECW driver itself.
> > >
> > > Even
> > >
> > > > Hi,
> > > >
> > > > I am having a bit of trouble with warping a dataset (an ECW file)
> with
> > > > multiple overviews. The base file is huge, so I am selecting the
> > > > overview that matches closest to my output resolution and makes an
> > > > in-memory VRT
> > >
> > > of
> > >
> > > > this, consisting of the overview bands of the original image.
> > > >
> > > > This seems to only work for some overview levels, and not for
> others. I
> > >
> > > get
> > >
> > > > results that appear to be made from the correct sets of colors
> > > > basically, but way out of scale and postion. Some times it seems to
> > > > work nicely though, so I suspect that there is some memory
> overwriting
> > > > issue or something here.
> > > >
> > > > This is the part of the code that builds the overview VRT. The input
> > > > dataset is _ds, an
> > > >
> > > > // Create a VRT of the closest matching overlay
> > > > GDALDriver *vrtDriver = (GDALDriver *) GDALGetDriverByName( "VRT" );
> > > >
> > > > vrtDS = vrtDriver->Create("", ovrW, ovrH, _numBands, _dataType,
> NULL);
> > > > GDALSetProjection(vrtDS, _srcProjectionWKT.c_str());
> > > >
> > > >    ouble geoTransform[6]; _ds->GetGeoTransform(geoTransform); double
> > > >
> > > > basePixelSizeX = geoTransform[XFM_PIXEL_SIZE_EW]; double
> basePixelSizeY
> > > > = geoTransform[XFM_PIXEL_SIZE_NS];
> > > >
> > > > geoTransform[XFM_PIXEL_SIZE_EW] = scaleX*basePixelSizeX;
> > > > geoTransform[XFM_PIXEL_SIZE_NS] = scaleY*basePixelSizeY;
> > > > vrtDS->SetGeoTransform(geoTransform);
> > > >
> > > > for(int i = 1; i <= _numBands; i++)
> > > > {
> > > > GDALRasterBand* srcRootBand = _ds->GetRasterBand(i);
> > > > GDALRasterBand* srcBand = srcRootBand->GetOverview(overviewId);
> > > > VRTSourcedRasterBand* vrtBand =
> > > > (VRTSourcedRasterBand*)vrtDS->GetRasterBand(i);
> > > > vrtBand->AddSimpleSource(srcBand);
> > > > }
> > >
> > > --
> > > Spatialys - Geospatial professional services
> > > http://www.spatialys.com
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
>
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