Hi Matthew, I've been working on "rolling/windowed" libraries for quite a while. I'm currently working on implementations for basic moment and rank statistics - they are pretty much done and I am trying to maneuver them into apache commons math for java. I am also interested in implementing these statistics for python/numpy and R. I have seen a little bit for R, but nothing yet for numpy. /brad On Nov 25, 2007 5:00 PM, Matthew Perry <perrygeo@gmail.com> wrote:

Hi all,

I'm not sure if my terminology is familiar but I'm trying to do a "moving window" analysis (ie a spatial filter or kernel) on a 2-D array representing elevation. For example, a 3x3 window centered on each cell is used to calculate the derivate slope of that cell.

Can this easily be implemented using numpy?

Currently I have tried implementing in pure python loops (too slow) and c++ (fast but more difficult to compile, distribute, wrap in python calls, etc). I think a good solution would be to leverage numpy which is both fast and and easy package for end users to install.

An example of the C++ code I'm trying to emulate is at http://perrygeo.net/download/hillshade.html . Does anyone have any tips or examples out there? Where should I start researching this?

-- Matthew T. Perry http://www.perrygeo.net _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion

Matthew Perry wrote:

Hi all,

I'm not sure if my terminology is familiar but I'm trying to do a "moving window" analysis (ie a spatial filter or kernel) on a 2-D array representing elevation. For example, a 3x3 window centered on each cell is used to calculate the derivate slope of that cell.

Can this easily be implemented using numpy?

If I understand you correctly, scipy.ndimage does exactly what you ask for. See http://www.scipy.org/SciPyPackages/Ndimage. Cheers, VS.