Translating concave hull algorithm to c#

Question

So I am trying to translate the algorith found here for concave hulls: http://repositorium.sdum.uminho.pt/bitstream/1822/6429/1/ConcaveHull_ACM_MYS.pdf

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Answer 1

I don't have the time right now to read the paper, but I assume from my knowledge of conVEX hull algorithms that you're going around the points in a particular direction looking for the next point to link to.

If that's the case, "angle" would be the angle of the most recent line segment of the hull, and you want to sort the points by their angle from that line. Therefore you want to calculate the angles between a line (on the hull) and a set of lines (from the current point to each other point being considered). Whether the angles calculated are positive or negative depends upon whether you're going clockwise or anticlockwise. To calculate the angles, look at something like this:

Calculating the angle between two lines without having to calculate the slope? (Java)

Then just sort by the angles.