Distance to horizon with terrain elevation data

Question

Looking for an algorithm to compute actual distance from a latitude/longitude/elevation to the visible horizon taking into account the actual surrounding terrain and the curve of the earth. Assume you have enough terrain data for the surrounding several hundred miles from any of the open elevation datasets. The problem can be simplified to an approximate by checking a few cardinal directions. Ideally I'd like to be able to compute the real solution as well.

Answer 1

Disclosure: I'm the developer and maintainer of the below mentioned software package.

I'm not sure if you're still looking for a solution as this question is already a bit older. However, one solution for your problem would be to apply the open-source package HORAYZON (https://github.com/ChristianSteger/HORAYZON). It's based on the high-performance ray tracing library Intel Embree (https://www.embree.org) and thus very fast and it considers Earth's curvature. With this package, you can compute the horizon angle and the distance to the horizon line for one or multiple arbitrary location(s) on a Digital Elevation Model (DEM) and set various options like the number of cardinal sampling directions, the maximal search distance for the horizon, etc. However - I'm not sure what you mean by "real solution". Do you mean the "perfect" solution - i.e. by considering elevation information from all DEM cells without doing a discrete sampling along the azimuth angle? Unfortunately, this cannot be done with the above mentioned package (but one could theoretically implement it).