The error message from afwDet.makeHeavyFootprint when the Footprint lies partially outside the image is:

OutOfRangeError('SpanSet bounding box lands outside array')

This is not very helpful. Please catch this error and include a more helpful message, indicating the top-level C++ routine (in this case makeHeavyFootprint), and the values of the SpanSet's bounding box and that of the image.

While working on this, please go through and look for other cases where the user would appreciate more information and fix them on this ticket.