Numpy and line intersections

Question

How would I use numpy to calculate the intersection between two line segments?

In the code I have segment1 = ((x1,y1),(x2,y2)) and segment2 = ((x1,y1),(x2,y2)). Note segment1 does not equal segment2. So in my code I've also been calculating the slope and y-intercept, it would be nice if that could be avoided but I don't know of a way how.

I've been using Cramer's rule with a function I wrote up in Python but I'd like to find a faster way of doing this.

Answer 1

Stolen directly from https://web.archive.org/web/20111108065352/https://www.cs.mun.ca/~rod/2500/notes/numpy-arrays/numpy-arrays.html

# # line segment intersection using vectors # see Computer Graphics by F.S. Hill # from numpy import * def perp( a ) :     b = empty_like(a)     b[0] = -a[1]     b[1] = a[0]     return b  # line segment a given by endpoints a1, a2 # line segment b given by endpoints b1, b2 # return  def seg_intersect(a1,a2, b1,b2) :     da = a2-a1     db = b2-b1     dp = a1-b1     dap = perp(da)     denom = dot( dap, db)     num = dot( dap, dp )     return (num / denom.astype(float))*db + b1  p1 = array( [0.0, 0.0] ) p2 = array( [1.0, 0.0] )  p3 = array( [4.0, -5.0] ) p4 = array( [4.0, 2.0] )  print seg_intersect( p1,p2, p3,p4)  p1 = array( [2.0, 2.0] ) p2 = array( [4.0, 3.0] )  p3 = array( [6.0, 0.0] ) p4 = array( [6.0, 3.0] )  print seg_intersect( p1,p2, p3,p4)