[gdal-dev] gdal_translate a VRT built on top of GeoTIFFs with NaN
Even Rouault
even.rouault at spatialys.com
Mon May 2 06:27:10 PDT 2016
Le lundi 02 mai 2016 15:16:30, Daniele Romagnoli a écrit :
> Hi Even,
> The produced GeoTIFF doesn't contain any nodata metadata/flag/TAG.
> It simply has "NaN" pixels. QuantumGIS report those pixels as "nan" and
> OpenEV report them as 1.#QNAN so I think they are properly "recognized" as
> NaN.
>
> I'm wondering if the GDAL utilities explicitly look for some metadata/flag
> (as the "nodata value" in your previous ascii based sample) to do noData
> checks or if it's also able to recognize a NaN "binary" value inside the
> pixels.
Yes, the NaN value must be explicitly set as the nodata property of the geotiff
file so that gdalbuildvrt can recognize it as the nodata value (similarly to
other nodata value)
You can do this with gdal_translate -a_nodata nan (or gdal_edit.py -a_nodata
nan)
>
> What do you think about it?
> Cheers,
> Daniele
>
> On Mon, May 2, 2016 at 2:52 PM, Daniele Romagnoli <
>
> daniele.romagnoli at geo-solutions.it> wrote:
> > Hi Even.
> > Thanks for the feedback.
> >
> > Sorry... I'm using GDAL 1.11.3.
> > I'm going to double check to make sure I didn't make any mistake.
> > I'll let you know.
> >
> > Cheers,
> > Daniele
> >
> >
> >
> > On Mon, May 2, 2016 at 2:49 PM, Even Rouault <even.rouault at spatialys.com>
> >
> > wrote:
> >> Le lundi 02 mai 2016 14:37:39, Daniele Romagnoli a écrit :
> >> > Hi List,
> >> >
> >> > I have a reprojectiion tool which creates GeoTIFFs with NoData = NaN.
> >> > I'm creating couple of GeoTIFFs with partially overlapping areas where
> >> > GeoTIFF1 has NaNs in a region and GeoTIFF2 has proper values in the
> >> > same overlapping region and viceversa (GeoTIFF2 has some NaN area
> >> > while
> >>
> >> GeoTIFF1
> >>
> >> > has valid pixels for same area).
> >> > I have built a VRT on top of them and then translated into a single
> >> > GeoTIFF. However, the result has NaN in those regions.
> >> > I was hoping that the area containing NaNs would have been ignored
> >>
> >> instead,
> >>
> >> > in favor of proper values from the other file.
> >> > Is there any flag, properties or suggestions to make it working?
> >> >
> >> > If I configure the reprojection tool to write NoData = -9999 and then
> >>
> >> use
> >>
> >> > gdalbuildvrt -srcnodata -9999, things are working fine.
> >> > So I'm just wondering if the same can be achieved dealing with NaN
> >>
> >> instead
> >>
> >> > of custom values.
> >>
> >> Daniele,
> >>
> >> You didn't mention which GDAL version you use. It is possible that
> >> support for
> >> NaN as a nodata value in gdalbuildvrt & the VRT driver was fixed at some
> >> point.
> >> From a quick test with trunk, it works (works with 1.11 branch as
> >> well):
> >>
> >> $ cat in1.asc
> >> ncols 3
> >> nrows 3
> >> xllcorner 440720.000000000000
> >> yllcorner 3750120.000000000000
> >> cellsize 60.000000000000
> >> NODATA_value nan
> >>
> >> 1.0 1.0 1.0
> >> 1.0 nan 1.0
> >> 1.0 1.0 1.0
> >>
> >> $ cat in2.asc
> >> ncols 3
> >> nrows 3
> >> xllcorner 440720.000000000000
> >> yllcorner 3750120.000000000000
> >> cellsize 60.000000000000
> >> NODATA_value nan
> >>
> >> nan nan nan
> >> nan 2.0 nan
> >> nan nan nan
> >>
> >> $ gdalbuildvrt nan.vrt in1.asc in2.asc
> >>
> >> $ gdal_translate nan.vrt /vsistdout/ -of aaigrid
> >> ncols 3
> >> nrows 3
> >> xllcorner 440720.000000000000
> >> yllcorner 3750120.000000000000
> >> cellsize 60.000000000000
> >> NODATA_value nan
> >>
> >> 1 1 1
> >> 1 2 1
> >> 1 1 1
> >>
> >> Even
> >>
> >> --
> >> Spatialys - Geospatial professional services
> >> http://www.spatialys.com
> >
> > --
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> > ==
> >
> > Ing. Daniele Romagnoli
> > Senior Software Engineer
> >
> > GeoSolutions S.A.S.
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