Curvature Function

[marcusspiegel]

I was looking into the code for the curvature function, and I noticed a few issues:

1. For McNab and Bolstad, 36.2 m is hard-coded in as the distance to the outermost cell, but shouldn't this vary with cell size and focal window size?
2. For McNab, it seems that x[5] is hard-coded into the function. This would be the central cell in a 3x3 window, but not larger windows? Or am I missing something?

Thanks!