[SciPy-Dev] Problem with N-dimensional interpolation using a new griddata function for N>=3

[Adam Machnik]

Hello ,

I have downloaded from SVN the latest `griddata` implementation for
working in N-D
with irregular grids (scipy v0.9.0dev6812).
It works great for 2D problems. However for 3D (and more) I have a problem:
the NaN values appears always in the same position, and it does not
depend on the scalar field being interpolated.
Here is a small example of simple 3x3x3 regular grid and a constant
scalar field of 1.0 values, that is interpolated at the input data
points.

Example:

******************************

from numpy import *
from scipy.interpolate import *

grid_x, grid_y, grid_z = mgrid[0:1:3j, 0:1:3j, 0:1:3j]

pts = [[ 0.0 , 0.0 , 0.0 ],
          [ 0.0 , 0.0 , 0.5 ],
          [ 0.0 , 0.0 , 1.0 ],
          [ 0.0 , 0.5 , 0.0 ],
          [ 0.0 , 0.5 , 0.5 ],
          [ 0.0 , 0.5 , 1.0 ],
          [ 0.0 , 1.0 , 0.0 ],
          [ 0.0 , 1.0 , 0.5 ],
          [ 0.0 , 1.0 , 1.0 ],
          [ 0.5 , 0.0 , 0.0 ],
          [ 0.5 , 0.0 , 0.5 ],
          [ 0.5 , 0.0 , 1.0 ],
          [ 0.5 , 0.5 , 0.0 ],
          [ 0.5 , 0.5 , 0.5 ],
          [ 0.5 , 0.5 , 1.0 ],
          [ 0.5 , 1.0 , 0.0 ],
          [ 0.5 , 1.0 , 0.5 ],
          [ 0.5 , 1.0 , 1.0 ],
          [ 1.0 , 0.0 , 0.0 ],
          [ 1.0 , 0.0 , 0.5 ],
          [ 1.0 , 0.0 , 1.0 ],
          [ 1.0 , 0.5 , 0.0 ],
          [ 1.0 , 0.5 , 0.5 ],
          [ 1.0 , 0.5 , 1.0 ],
          [ 1.0 , 1.0 , 0.0 ],
          [ 1.0 , 1.0 , 0.5 ],
          [ 1.0 , 1.0 , 1.0 ]]

vls = ones(27)

points = array(pts).astype('float64')
values = array(vls).astype('float64')

grid_z1 = griddata(points, values, (grid_x, grid_y, grid_z),
method='linear', fill_value=0)

print 'grid_z1=', grid_z1

***********************

I obtain the following result:

grid_z1= [[[  1.   1.   1.]
  [  1.   1.   1.]
  [  1.   1.   1.]]

 [[  1.   1.   1.]
  [  1.   1.   1.]
  [  1.   1.   1.]]

 [[  1.   1.   1.]
  [  1.   1.  nan]
  [  1.   1.   1.]]]


Thanks,

Adam