[ryanbberger]

It was definitely quite a bit of effort to get every line of sight. We felt it was necessary if we were going to try and prove that there are none longer.

Regular viewshed algorithms really aren't built for it, and being able to do it cheaply while also maintaining a cluster of compute that can shut down at any time is also its own mess (these were all spot instance so we could get 75+% off).

The 530km number takes into account both the curvature, along with refraction. It's a simple elevation adjustment when you are doing your angle of elevation calculations.

If you want a synopsis of how we calculate lines of sight and all the parameters we use I have a shorter, less whitepaper-y blog post here:

https://ryan.berge.rs/posts/lines-of-sight/