additional diff_from_x function ideas

[AndrewAnnex]

I am working on a project where I am attempting to measure thicknesses of layers in an eroded layered landscape and I have been playing with DiffFromMeanElev which is almost doing exactly what I think I need. I was wondering if it would be possible to add new functions DiffFromMaxElev/DiffFromMinElev to instead compute the maximum/minimum of the local neighborhood and then for each pixel get the difference from that value. This could allow one to determine a lower boundary of thickness provided an elevation low was close enough to an elevation peak without worrying about larger scale topographic trends. If there is a way to achieve this with existing methods that would be great to know