check points inside triangle or on edge with example
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Roger Stafford on 9 Apr 2016
Suppose P1 = [x1,y1], P2 = [x2,y2], and P3 = [x3,y3] are row vectors giving the coordinates of the three vertices of a triangle, and P = [x,y] is a row vector for the coordinates of a point P. To determine whether P lies inside the triangle P1P2P3 do this:
P12 = P1-P2; P23 = P2-P3; P31 = P3-P1;
t = sign(det([P31;P23]))*sign(det([P3-P;P23])) >= 0 & ...
sign(det([P12;P31]))*sign(det([P1-P;P31])) >= 0 & ...
sign(det([P23;P12]))*sign(det([P2-P;P12])) >= 0 ;
Point P lies within the triangle if and only if t is true.