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

[Thomas Sevaldrud]

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.

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.

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.

- 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
>
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