块状和直线相交

直接从http://www.cs.mun.ca/~rod/2500/notes/numpy-arrays/numpy-
arrays.html
失窃

## 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 + b1p1 = 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)