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

[Pietro]

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