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<mailto: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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