I'm trying to learn Computational Geometry and this formula isn't obvious to me.

Hint: cross is related to the cross product of two vectors.

# Returns intersection of infinite lines ab and pq (or undefined)
point intersect(point a, point b, point p, point q):
    d1 = cross(p - a, b - a)
    d2 = cross(q - a, b - a)
    return (d1 * q - d2 * p) / (d1 - d2)
  • 1
    $\begingroup$ It's not clear what you're asking. Do you know what the cross function does? Do you understand what the intersect function does? $\endgroup$
    – Pål GD
    Jun 16, 2020 at 12:51
  • $\begingroup$ Thanks for response .... I mean i need the proof of correctness of this method ... I try some values and it works but how ? I always solve it by solving two algebraic equations of the two lines . $\endgroup$ Jun 16, 2020 at 15:23
  • $\begingroup$ I'd suggest looking at this: stackoverflow.com/questions/563198/… $\endgroup$
    – user
    Jun 16, 2020 at 21:24
  • $\begingroup$ helpful, thanks . $\endgroup$ Jun 17, 2020 at 11:39


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