griddata runtime error -- Python / SciPy (Interpolation)

I use scipy's griddate-function for interpolation.

What does the following error message means which appears when python is executing the griddata-function?

File "C:\Python25\lib\site-packages\scipy\interpolate\ndgriddata.py", line 182, in griddata
ip = LinearNDInterpolator(points, values, fil开发者_开发问答l_value=fill_value)
File "interpnd.pyx", line 192, in interpnd.LinearNDInterpolator.__init__ (scipy\interpolate\interpnd.c:2524)
File "qhull.pyx", line 917, in scipy.spatial.qhull.Delaunay.__init__ (scipy\spatial\qhull.c:4030)
File "qhull.pyx", line 170, in scipy.spatial.qhull._construct_delaunay (scipy\spatial\qhull.c:1269)
RuntimeError: Qhull error

This typically means that the point set you passed in cannot be triangulated. Some common cases when this might occur:

• You have 2D data, but all the points lie along a line. In this case there is no triangulation of the data to non-degenerate triangles.
• You have 3D data, but all the points lie on a plane, so no decomposition to non-degenerate tetrahedra. And so on to higher dimensions.

In these cases, interpolation does not make sense either, so this failure is not an indication of a bug, but incorrect usage of griddata.

Typically, Qhull prints additional information on what went wrong to stderr, so check the program output to see what it says.

This indicates that the qhull (http://www.qhull.org) code which is used by the function is not returning a result because of an error.

Does this always happen, or only for certain inputs?

Can you post an example input which causes the error?