[gdal-dev] java Dataset.GetRasterBand(i).ComputeRasterMinMax not working for float data

[mccorb]

If you like I can upload the file and send you a google drive link if you
give me the email you want to receive it from.

Thanks,

On Fri, Jan 27, 2017 at 1:34 PM, Even Rouault-2 [via OSGeo.org] <
ml-node+s1560n5305129h58 at n6.nabble.com> wrote:

> On vendredi 27 janvier 2017 12:25:43 CET mccorb wrote:
>
> > Even,
>
> >
>
> > I agree but the call to ComputeRasterMinMax() contains nodata values for
>
> > the min. It doesn't do the downcast correctly.
>
>
>
> What does gdalinfo -mm report ?
>
>
>
> >
>
> > thanks,
>
> >
>
> > On Fri, Jan 27, 2017 at 12:38 PM, Even Rouault-2 [via OSGeo.org] <
>
> >
>
> > [hidden email] <http:///user/SendEmail.jtp?type=node&node=5305129&i=0>>
> wrote:
>
> > > On vendredi 27 janvier 2017 11:15:59 CET mccorb wrote:
>
> > > > I have a geotiff image with float data (GDT_Float32). When I read a
> tile
>
> > >
>
> > > I
>
> > >
>
> > > > have to case the nodata value to float to make it compare otherwise
> it
>
> > > >
>
> > > > doesn't...here is a reduced snippet of my code
>
> > > >
>
> > > >
>
> > > >
>
> > > > Double[] d = new Double[1];
>
> > > >
>
> > > > rb.GetNoDataValue(d);
>
> > > >
>
> > > > double noDataVal = d[0];
>
> > > >
>
> > > > ...
>
> > > >
>
> > > > if(rasterBandDataType == gdalconstConstants.GDT_Float32)
>
> > > >
>
> > > > {
>
> > > >
>
> > > > float[] array = new float[(rect.height * rect.width)];
>
> > > >
>
> > > > int retVal = rb.ReadRaster(rect.x, rect.y, rect.width, rect.height,
>
> > > >
>
> > > > rasterBandDataType, array);
>
> > > >
>
> > > > * float noDataValCast = (float) noDataVal;*
>
> > > >
>
> > > > for(int i = 0; i < array.length; i++)
>
> > > >
>
> > > > {
>
> > > >
>
> > > > if(noDataValCast == buff[i])
>
> > > >
>
> > > > array[i] = Double.NaN;
>
> > > >
>
> > > > else
>
> > > >
>
> > > > array[i] = (scale * buff[i]) + offset;
>
> > > >
>
> > > > }
>
> > > >
>
> > > > }
>
> > > >
>
> > > >
>
> > > >
>
> > > > If I don't cast the noDataVal to a float then the value in the
> returned
>
> > > >
>
> > > > array doesn't equal the noData value
>
> > > >
>
> > > > returned from the raster band.
>
> > > >
>
> > > >
>
> > > >
>
> > > > It seems as though the ComputeRasterMinMax call has the same issue
> as I
>
> > >
>
> > > was
>
> > >
>
> > > > having before I did the casting. I definitely want to use this
> method it
>
> > > >
>
> > > > because it is much faster than pulling the tiles and processing them
>
> > >
>
> > > myself.
>
> > >
>
> > >
>
> > >
>
> > > All of that is more or less expected given that GetNoDataValue() and
>
> > > ComputeRasterMinMax() return double values. So if you compare to float
>
> > > directly, the float get promoted to double (and the double isn't
> strictly
>
> > > equal to the initial pixel value), and tiny precision issues appear.
>
> > > Downcasting to float as you did is the way to go.
>
> > >
>
> > >
>
> > >
>
> > > Even
>
> > >
>
> > >
>
> > >
>
> > > --
>
> > >
>
> > > Spatialys - Geospatial professional services
>
> > >
>
> > > http://www.spatialys.com
>
> > >
>
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>
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>
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>
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