[gdal-dev] why do I get a floating point nodata value from a byte raster?

[Even Rouault]

Selon Richard Sharp <richsharp at stanford.edu>:

> On Fri, Aug 29, 2014 at 10:34 AM, Even Rouault <even.rouault at spatialys.com>
> wrote:
>
> > Le jeudi 28 août 2014 23:32:38, Richard Sharp a écrit :
> > > I have a byte GTiff dataset that has a nodata value of 0 according to
> > QGIS.
> >
> > Well, I've just created such a file, and with QGIS 1.8, the GUI display
> > well
> > the -3.4028230607370965e+38 value, but with 2.4, it displays 0. So seems
> > to be
> > on QGIS side.
> > That said,  -3.4028230607370965e+38 doesn't make sense as a nodata value
> > for
> > Byte, which can only range from 0 to 255.
> > After some testing, it seems that QGIS displays 0 when the nodata value is
> > out
> > of the range of the data type.
> >
> >
> Thanks Evan.  Just so I'm clear, you're saying that the raster had its
> nodata value set to something that exceeded its datatype range.

Yes.

  In that
> case, it doesn't make sense to interpret the  -3.4028230607370965e+38 as
> "0" in the byte range,

Yes, QGIS should ignore the nodata value, as if there was nodata reported

> but rather as a nodata value defined for the valid
> pixels in the raster?

I've not verified if it actually takes 0 as a nodata value, but if it does, yes
that's unexpected.

>


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