[GRASS-user] Read/Write numpy array

[Johannes Radinger]

Hello Glynn,
Hello Josef,

Thank you for your answer but I still get an error, although I changed the code
which is now:
    x = garray.array()
    x.read("distance_raster")
    Density = garray.array()
    Density[...] = p * stats.norm.pdf(x,loc=m, scale=s1*K) + (1-p) * stats.norm.pdf(x, loc=m, scale=s2*K)
    Density.write("Density")

the error says:
   Density[...] = p * stats.norm.pdf(x,loc=m, scale=s1*K) +
(1-p) * stats.norm.pdf(x, loc=m, scale=s2*K)
  File "/Library/Frameworks/Python.framework/Versions/2.6/li
b/python2.6/site-packages/scipy/stats/distributions.py",
line 1104, in pdf
    x = arr((x-loc)*1.0/scale)
TypeError: unsupported operand type(s) for /:
'numpy.ndarray' and 'numpy.ndarray'


Propably it has something to do with the stats-norm function of scipy which is working
with numpy array (maybe not with the garray)..or what does that error mean?


PS: @ You once helped me with this scipy equation I now want to use within a python-GRASS-GIS script.
Transforming a raster-map into an array and apply the scipy-function on it and transform it back to a raster.
Maybe you have some ideas what is the problem...


Am 05.04.2011 um 19:43 schrieb Glynn Clements:

> 
> Johannes Radinger wrote:
> 
>> I try to do a mapcalculation with scipy (do to limited functionality of 
>> usual mapcalc functions.
>> 
>> Therefore I want to read a map into numpy-array, do the calculation
>> on it and write it back to a GRASS-map. I tried to follow the
>> instructions in the wiki
>> (http://grass.osgeo.org/wiki/GRASS_and_Python#Interfacing_with_NumPy)
>> but I got stucked when it comes to the writing-process.
>> Thats my code so far:
>> 
>>    x = garray.array()
>>    x.read("distance_raster")
>>    Density = garray.array()
>>    Density = p * stats.norm.pdf(x,loc=m, scale=s1*K) + (1-p) * stats.norm.pdf(x, loc=m, scale=s2*K)
>>    Density.write("Density")
>> 
>> The stats.norm.pdf is from the stats-scipy module. I get following
>> error when I try to process the script:
>> 
>>   Density.write("Density")
>> AttributeError: 'numpy.ndarray' object has no attribute
>> 'write'
>> 
>> I don't know excactly what how I have to use the write command.
> 
> The write() method is part of garray.array, which is a subclass of
> numpy.array (specifically, of numpy.memmap).
> 
> This line:
> 
>>    Density = garray.array()
> 
> creates an instance of garray.array and associates the name "Density"
> with it.
> 
> This line:
> 
>     Density = p * stats.norm.pdf(x,loc=m, scale=s1*K) + (1-p) * stats.norm.pdf(x, loc=m, scale=s2*K)
> 
> creates a normal numpy.array and associates the name "Density" with
> it, replacing the original association. Consequently, Density.write()
> fails because Density now refers to a numpy.array and not a
> garray.array().
> 
> Rather than making the name Density refer to the resulting
> numpy.array, you have to assign the resulting numpy.array *into* the
> existing garray.array to which the name Density already refers, i.e.:
> 
>     Density[...] = p * stats.norm.pdf(x,loc=m, scale=s1*K) + (1-p) * stats.norm.pdf(x, loc=m, scale=s2*K)
> 
> Note that the "..." (ellipsis) is literal. The above is equivalent to:
> 
>     Density[:,:] = p * stats.norm.pdf(x,loc=m, scale=s1*K) + (1-p) * stats.norm.pdf(x, loc=m, scale=s2*K)
> 
>> I am working on 6.5 and I read there were some problems with
>> numpy-arrays. Are the solved now?
> 
> I believe that the issue with grass.script.array requiring the 7.0
> version of r.{in,out}.bin has been solved by backporting the changes
> into 6.5.
> 
> -- 
> Glynn Clements <glynn at gclements.plus.com>
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user