Observations

1. R is like an autocorrelation distance for visibility.
2. Increasing R emphasizes global features.
3. Increasing R generally lowers visibilities.
4. Increasing H generally raises visibilities.
5. Increasing H blurs the visibilities.
6. Increasing H somewhat preserves relative visibilities.
7. For fixed R,H, there may be little relation between a point's elevation and its visibility.
8. Indeed, lower points may be more visible.