Function G2lib::isCounterClockwise

Function Documentation

int_type G2lib::isCounterClockwise(real_type const *P1, real_type const *P2, real_type const *P3)

Return the orientation of a triangle

return +1 = CounterClockwise return -1 = Clockwise return 0 = flat

CounterClockwise: the path P1->P2->P3 turns Counter-Clockwise, i.e., the point P3 is located “on the left” of the line P1-P2. Clockwise: the path turns Clockwise, i.e., the point P3 lies “on the right” of the line P1-P2. flat: the point P3 is located on the line segment [P1 P2].

Algorithm from FileExchage geom2d adapated from Sedgewick’s book.

Parameters

  • P1 – [in] first point of the triangle

  • P2 – [in] second point of the triangle

  • P3 – [in] third point of the triangle

Returns

sign of rotation