[GRASS-dev] Extracting coordinates of RasterNumpy objects (pygrass)

[Pierre Roudier]

Thanks Pietro,

Yes that answers the question, but just partly: I was actually
wondering whether it would be possible to get the extracted x and y
coordinates in geographic space (as opposed to the Numpy array space)?

Thanks again for the great work on pygrass,

P

2012/12/17 Pietro <peter.zamb at gmail.com>:
> Hi Pierre,
>
> On Mon, Dec 17, 2012 at 7:48 AM, Pierre Roudier
> <pierre.roudier at gmail.com> wrote:
>> Hi,
>>
>> I am using (with enthusiasm!) Pietro's pygrass library to develop a raster
>> module. I am using Numpy/Scipy as my working horse, so I manipulate a lot of
>> the RasterNumpy objects that have been introduced with pygrass.
>
> I'm really happy that you are using the pygrass library! ;-)
>
>
>> In a specific step, I am identifying pixels using a test (this would be
>> similar to my_array <  100). I would like to extract the points that satisfy
>> the test, and access not only their values and index in the array, but I
>> would also go back to their coordinates to extract them as (x, y, z).
>>
>> Is there a way to do this using RasterNumpy and pygrass?
>
> yes, you should use the numpy stuff, something like:
>
>>>> import numpy as np
>>>> a = np.arange(15).reshape(3, 5)
>>>> a
> array([[ 0,  1,  2,  3,  4],
>        [ 5,  6,  7,  8,  9],
>        [10, 11, 12, 13, 14]])
>>>> b = a>7
>>>> b1
> array([[False, False, False, False, False],
>        [False, False, False,  True,  True],
>        [ True,  True,  True,  True,  True]], dtype=bool)
>>>> b.nonzero()  # return two array with x and y and z if the array is 3D
> (array([1, 1, 2, 2, 2, 2, 2]), array([3, 4, 0, 1, 2, 3, 4]))
>
> Please let me know if you find something that is not clear, or is not
> working properly...
>
> All the best!
>
> Pietro



-- 
Scientist
Landcare Research, New Zealand