[gdal-dev] gdal_translate a VRT built on top of GeoTIFFs with NaN
Even Rouault
even.rouault at spatialys.com
Mon May 2 06:42:24 PDT 2016
Le lundi 02 mai 2016 15:37:58, Daniele Romagnoli a écrit :
> On Mon, May 2, 2016 at 3:27 PM, Even Rouault <even.rouault at spatialys.com>
>
> wrote:
> > 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)
>
> Ok. Thanks.
> I was trying to add it with "gdalbuildvrt -srcnodata nan" to avoid an
> intermediate step between my geotiff and the VRT but I was getting:
> ERROR 5: Invalid -srcnodata value
>
> Therefore, I had to edit the VRT by replacing the
> <ComplexSource><NODATA>-9999</NODATA></ComplexSource> with "nan" instead of
> "-9999".
> Do you know if there is any chance to let the -srcnodata parameter accept a
> String like "nan"?
Yes, this is available in the fresh new 2.1.0:
* gdalbuildvrt: accept nan as value for -srcnodata and -vrtnodata
>
> Cheers,
> Daniele
>
> > > 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
> > > >>
> > > >> --
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