Alphashape, but minimal implementation, fast checking if point is inside the shape
Note:
- alpha value takes the reciprocal, just to agree with the alphashape lib from pip
- this api only has 'point_in_shape' method
- the alphashape may contain a hole inside
Tested on a shape with ~20000 points, ~26000 triangles. Took me less than 1 min to create a 843x1218 mask. (updated)