OJ cannot handle tags into GeoTIFF, I think, except world coordinates. I
wonder if we can extend to OJ this GDAL capability.
It seems more simple to extend the external xml auxilary file to nodata. We
should also implement OJ to recognize a certain value as no data on
reading/writing either like Sextante (user can define an arbitrary no data
value) or as an internal one:like SAGA -99999 or ESRI -9999.
Thanks Jukka for the clarification
Peppe
2015-02-26 14:11 GMT+01:00 Rahkonen Jukka (MML) <
jukka.rahko...@maanmittauslaitos.fi>:
> Hi,
>
>
>
> GDAL seems to handle nodata this way:
>
>
>
> In case of GeoTIFF read http://www.gdal.org/frmt_gtiff.html: GDAL stores
> band nodata value in the non standard TIFFTAG_GDAL_NODATA ASCII tag (code
> 42113) for files created with the default profile GDALGeoTIFF. Note that
> all bands must use the same nodata value. When BASELINE or GeoTIFF profile
> are used, the nodata value is stored into a PAM .aux.xml file.
>
>
>
> If that tag is found from GeoTIFF GDAL knows what to do. Other programs
> not necessarily, here is an example from listgeo utility:
>
> listgeo test.tif
>
> TIFFReadDirectory: Warning, Unknown field with tag 42113 (0xa481)
> encountered.
>
>
>
> NoData value can be routed into an external xml metadata file with a
> command like this:
>
> gdal_translate -of gtiff -co profile=geotiff italy.tif nodata3.tif
> -a_nodata 3
>
>
>
> The resulting nodata3.tix.aux.xml file looks like this:
>
> <PAMDataset>
>
> <PAMRasterBand band="1">
>
> <NoDataValue>3.00000000000000E+000</NoDataValue>
>
> </PAMRasterBand>
>
> </PAMDataset>
>
>
>
>
>
> -Jukka Rahkonen-
>
>
>
>
>
> Stefan Steiniger wrote:
>
>
>
> Hi Peppe and others,
>
> OJ doesn't understand no-data (in terms of registering -9999 and
> converting it), as you can also see when colour theming vector data with
> classification (it is not possible to exclude certain values).
>
> I believe I personally tried to use also unrealistic values such as the
> -9999 in implementations. But, as there is/was no OJ standard, it is up to
> the plugin author. So, its probably a bit messy at the moment. However, I
> guess Sextante has a standard on it?
> Btw. for vector attributes I also tried using "Double.NaN" for null or
> in-valid values, which is not possible everywhere (e.g. one needs to know
> that it is Double value).
>
> Perhaps we should/can define amn OJ standard on that? However, the problem
> comes then also with writing the data. I.e. when you give the data to
> someone with his own program...
>
> Perhaps Jukka knows a about how other programs handle this?
>
> cheers,
> stefan
>
>
> On 02/25/2015 10:38 AM, Giuseppe Aruta wrote:
>
> Sorry, I forgot the core argument: I was talking about TIFF images
> loaded by RasterImageLayer.class ( so called "Open Sextante Raster Image"
>
> Peppe
>
>
>
> 2015-02-25 11:56 GMT+01:00 Giuseppe Aruta <giuseppe_ar...@yahoo.it>:
>
> Hi,
>
> I use OJ/Sextante for spatial analysis on DEM. And recently I wanted to
> extend OJ raster capabilities to make it more flexible.
> In some occasion I checked that OJ doesn't handle NonData value very well,
> for instance a)on displaying on workbench or b) on querying raster info,
> ex.using the new tool Raster>Raster statistics {Which I made :-( } .
> In several times OJ reads NoData value as the minimun value - it is the
> experience of the user to understand and try to solve it.
> Grid files have not such problem (FLT or ASC, handled by OJ) as NoDat is
> written into the headers.
>
> How does OJ handle nodata values?
>
> Does OJ recognize only the standard ESRI -9999 value or even any other
> arbitrary nodata values (SAGA -999999? In may occasion I found elevation
> DEM where the nodata value was set to 0, you can understand when this DEM
> are used for slope or aspect maps!)?
>
> Can we handle nodata on TIFs, maybe using the auxiliary XML file (thanks
> Alberto's job)?
>
>
>
> Thanks in advance for the answer. It would be fine for me if I have a help.
>
> Giuseppe Aruta
>
>
>
>
>
>
>
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