如何检查一个点是否在由另外两个点定义的线上？

Question

I'm writing a program in python that needs to determine if a point is on an infinite line formed by two other points. I found many other questions asking about line segments, but I need an infinite line.

Answer 1

You can try something like this:

# positive when P is on the left of oriented line AB, 
# neutral when P lies on AB,
# negative when P is on the right of oriented line AB
def half_space(pX, pY, aX, aY, bX, bY):
    return (bX - aX)*(pY - aY) - (bY - aY)*(pX - aX)