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

[mccorb]

Even,

I agree but the call to  ComputeRasterMinMax() contains nodata values for
the min. It doesn't do the downcast correctly.

thanks,

On Fri, Jan 27, 2017 at 12:38 PM, Even Rouault-2 [via OSGeo.org] <
ml-node+s1560n5305119h48 at n6.nabble.com> 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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