Hi Stefan,
User can define a default nodata value on Sextante (Sextante
Toolbar>Setting>General). The problem is that this value is applied to any
raster used in Sextante excluding other values that come from file header.
This mean that:
a) for every analysis on a single raster file, user should know before
the exact nodata value of the file and set sextante setting on it (nodata
value of file = nodata value on Sextante setting).
b) if user want to do a raster algebra with more than 2 raster files, all
noata value should set to the same values (nodata 1st file = nodta 2nd file
= nodata Sextante setting).
Point b) has no solution on actual OJ/Sextante equipement (except manually
changing nodata header and values on .asc files).
If we reduce the term of discussion to TIF files, it becomes more
difficult.
I found this dirty strategy, probably long but effective.
User inspect TIF raster to find "unusual" values, generally on the border,
usually equal to "0". They save it to .asc (plugin still not available, I
hope to put on OJ as soon as possible). Open the .asc file with a text
editor and a) change "NoData" value to "-9999" b) find/substitute "O" to
"-9999".
A shorter and more elegant strategy should pass through the usage of
dedicated plugins
Peppe
2015-02-25 21:44 GMT+01:00 Stefan Steiniger <sst...@geo.uzh.ch>:
> 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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