Topographic Horizons

Computes the angles to the horizons from an elevation grid, measured in degrees upward from the horizontal, with options for parallelism.

This set of functions, based on a paper submitted to IEEE Geoscience and Remote Sensing Letters [1], computes the angles to the horizons from an elevation grid, measured in degrees upward from the horizontal. The one-dimensional problem uses an order N algorithm [2]. Horizons for arbitrary azimuths are derived by rotating the elevation grid, then calculating the horizons along the columns of the rotated grid and re-rotating the grid back to its original orientation. The code supports grids in either projected or geographic format; it also calculates the distances to the horizon. One of the demo illustrations uses my Sun Position toolbox, but the needed functions are included here too.

[1] J. Dozier, Revisiting the topographic horizon problem in the era of big data and parallel computing, IEEE Geosci. Remote Sens. Lett., 2022, doi: 10.1109/LGRS.2021.3125278.

[2] J. Dozier, J. Bruno, and P. Downey, "A faster solution to the horizon problem," Comp. Geosci., 7, 145-151, 1981, doi: 10.1016/0098-3004(81)90026-1.