javascript - How to compute an angle between 2 vectors in a polygon -


i implemented method in javascript compute angle between 2 vectors. don't know how compute angle lies in polygon.

example example, in image want compute red angle in left 1 need go ac ab while in right 1 need ab ac.

thank response

from question understand need values of red (internal) angles. easy them knowing order. ccw order find directed angle between 2 consecutive edge vectors. in first case vectors ba/ac, in second ca/ab

to directed angle in full 2*pi (360 degrees) range, can use atan2 function

fi_left = atan2 (crossproduct(ba, ac), dotproduct(ba, ac))     fi_right = atan2 (crossproduct(ca, ab), dotproduct(ca, ab))

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