My solution is here. I actually documented the approach in pt1 / pt2 at the top. I won’t paste it here to avoid spoilers, it’s still early on the day.

Source at https://gist.github.com/ferd/fa1618fbdbbfa0b4c7fb01a74d35463f

My solution : https://github.com/cblavier/advent/tree/master/lib/2019/day10

Wasted at least 1 hour this morning going totally wrong (I was only dealing with 8 different angles)

And then I used the high school maths mentioned by @ferd

Interestingly, this can be solved without atan or any other float arithmetic. Here is a StackOverflow answer with an example algorithm for sorting points (the key is cross product of vectors).

Part 1 and Part 2 (most days, I clone my Part 1 solution before starting on Part 2, to preserve it as it was).

I kinda like how this one turned out. Less brute-force-y than most of my other solutions, but boy did it take a long time to get there.