[gdal-dev] ASCII Rasters and 'null' values in python-gdal

[Oz Nahum]

Hi, Thanks for the answer.
Ok, I admit the way I presented my first email is a bit confusing.
But the problem is not with the 'null' values. Rather the problem is with
the raster containing the no data values as -9999. This is a no data
representation like you said.
My problem is that GDAL is converting the last -9999 value to this value
31081.
raster2.asc and looks like this:
in text editor:
ncols         6
nrows         4
xllcorner     3366820.0000019
yllcorner     5814589.0300007
cellsize      10
NODATA_value -9999
1 1 1 1 1 1
1 1 1 1 1 1
1 1 1 1 1 1
1 1 1 1 -9999 -9999in python:
>>> dataset = gdal.Open('raster1.asc', GA_ReadOnly)
>>> a = gdal_array.DatasetReadAsArray(dataset)
>>> a
array([[    1,     1,     1,     1,     1,     1],
       [    1,     1,     1,     1,     1,     1],
       [    1,     1,     1,     1,     1,     1],
       [    1,     1,     1,     1, -9999, 31081]], dtype=int16)
>>>

Thanks again,
Oz.

On Fri, Feb 27, 2009 at 3:26 AM, Chaitanya kumar CH
<chaitanya.ch at gmail.com>wrote:

> Oz,
>
> NODATA_VALUES is supposed to be a pixel value (integer or real)
> whereas "null" is a string. Try to convert all the "null" strings into
> an unused pixel value like -9999 in raster1.asc
>
> Regards,
> --
> Chaitanya kumar CH.
>
> On Fri, Feb 27, 2009 at 2:34 AM, Oz Nahum <nahumoz at gmail.com> wrote:
> > Hi,
> > I have to ascii raster that I created using a text editor:
> > the first is called raster1.asc and looks like this:
> > ncols         6
> > nrows         4
> > xllcorner     3366820.0000019
> > yllcorner     5814589.0300007
> > cellsize      10
> > NODATA_value  -9999
> > 1 1 1 1 1 1
> > 1 1 1 1 1 1
> > 1 1 1 1 1 1
> > 1 1 1 1 -9999 -9999
> > The second is called raster2.asc and looks like this:
> > ncols         6
> > nrows         4
> > xllcorner     3366820.0000019
> > yllcorner     5814589.0300007
> > cellsize      10
> > NODATA_value  null
> > 1 1 1 1 1 1
> > 1 1 1 1 1 1
> > 1 1 1 1 1 1
> > 1 1 1 1 null null
> >
> > When I import them into python I find out the lower right corner of the
> > first raster is not giving the correct value: instead of 'null' qgis
> > displays the value '31081'.
> > The other raster is imported correctly and it showing 'null's for the two
> > last data cells.
> >
> >>>> dataset = gdal.Open('raster2.asc', GA_ReadOnly)
> >>>> b = gdal_array.DatasetReadAsArray(dataset)
> >>>> b
> > array([[1, 1, 1, 1, 1, 1],
> >        [1, 1, 1, 1, 1, 1],
> >        [1, 1, 1, 1, 1, 1],
> >        [1, 1, 1, 1, 0, 0]], dtype=int16)
> >>>> dataset = gdal.Open('raster1.asc', GA_ReadOnly)
> >>>> a = gdal_array.DatasetReadAsArray(dataset)
> >>>> a
> > array([[    1,     1,     1,     1,     1,     1],
> >        [    1,     1,     1,     1,     1,     1],
> >        [    1,     1,     1,     1,     1,     1],
> >        [    1,     1,     1,     1, -9999, 31081]], dtype=int16)
> >>>>
> >
> >
> > So before I go and open a bug, I just wanted to know - what is wrong ?
> Maybe
> > it's my system setup ? Maybe i don't write correct ascii rasters ? Also,
> > another thing I would like to bypass is the fact that 'null' values are
> > formed as zeros in gdal-numpy - this could lead to error when doing some
> > raster manipulations. Is there a way to by pass this (besides being
> > aware...)?
> >
> > I use Debian Lenny the latest relevant packages from.
> >
> > Thanks,
> > Oz N,
> > Grad Studend,
> > Universität Tübingen
> >
> >
> >
> > --
> >
> > ----
> >            Imagine there's no countries
> >            It isn't hard to do
> >            Nothing to kill or die for
> >            And no religion too
> >            Imagine all the people
> >            Living life in peace
> > ----
> >           You all must read 'The God Delusion'
> >           http://en.wikipedia.org/wiki/The_God_Delusion
> > ---
> > when one person suffers from a delusion it is called insanity. When many
> > people suffer from a delusion it is called religion."
> > Robert Pirsig, Zen and the Art of Motorcycle Maintenance
> >
> >
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >
>



-- 

----
           Imagine there's no countries
           It isn't hard to do
           Nothing to kill or die for
           And no religion too
           Imagine all the people
           Living life in peace
----
          You all must read 'The God Delusion'
          http://en.wikipedia.org/wiki/The_God_Delusion
---
when one person suffers from a delusion it is called insanity. When many
people suffer from a delusion it is called religion."
Robert Pirsig, Zen and the Art of Motorcycle Maintenance
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