changing a circular aperture to square

Hi... I have a script that takes a circular aperture and moves it through a raster pattern. I would like to redefine the aperture as a square. I am stumped for some reason. Any help is appreciated.

thanks.

Brian

[Walter Roberson]

We will probably need to see the code, to see how the aperture is being implemented.

[Image Analyst]

And a screenshot, image, diagram, plot, or anything else that will help illustrate the problem.