interpolation fails for irregularly spaced point cloud

[baagaard]

Interpolation can fail when point cloud contains irregularly spaced points. Position of points relative to grid can matter, because we select the points for interpolation based on the distance from the given point.

Because we don't generate topology information for the point cloud, a good solution in this case would be to use radial basis functions. This would result in a much more robust interpolation algorithm. See issue #1.

Reported by Jeanne Sauber