I tested your function by 2 samples. One returned the overlap polygon
successfully. but the second one failed. is there anything wrong in my
code?

thank you in advance.

pro test_polygon_overlap

   shape1 = fltarr(2,4)
   shape2 = fltarr(2,4)
   shape1[0,0] = 0.1
   shape1[0,1] = 1.1
   shape1[0,2] = 1.2
   shape1[0,3] = 0.2
   shape1[1,0] = 0.2
   shape1[1,1] = 0.15
   shape1[1,2] = 1.1
   shape1[1,3] = 1.2

   shape2[0,0] = 0.5
   shape2[0,1] = 1.5
   shape2[0,2] = 1.6
   shape2[0,3] = 0.4
   shape2[1,0] = 0.5
   shape2[1,1] = 0.6
   shape2[1,2] = 1.7
   shape2[1,3] = 1.5

   shape3 = shape_overlap (shape1, shape2, exists = exs)

   print, exs

shape1 = fltarr(2,17)
shape1 [*,0]  = [116.44991,41.441910]
shape1 [*,1]  = [116.57357,41.374821]
shape1 [*,2]  = [116.64723,41.312994]
shape1 [*,3]  = [116.57488,41.002544]
shape1 [*,4]  = [116.36967,40.928878]
shape1 [*,5]  = [116.16840,40.984128]
shape1 [*,6]  = [116.21576,41.053847]
shape1 [*,7]  = [116.06185,41.099889]
shape1 [*,8]  = [116.10263,41.168293]
shape1 [*,9]  = [116.13683,41.214334]
shape1 [*,10] = [116.16577,41.264322]
shape1 [*,11] = [116.18156,41.319572]
shape1 [*,12] = [116.22891,41.344565]
shape1 [*,13] = [116.31442,41.357720]
shape1 [*,14] = [116.29337,41.387976]
shape1 [*,15] = [116.34468,41.422178]
shape1 [*,16] = [116.44991,41.441910]

shape2 = fltarr(2,6)
shape2 [*,0] = [116.21839,41.528731]
shape2 [*,1] = [116.61698,41.524784]
shape2 [*,2] = [116.72748,41.141984]
shape2 [*,3] = [116.30916,41.203810]
shape2 [*,4] = [116.13552,41.289316]
shape2 [*,5] = [116.21839,41.528731]

xrange = [116.06185 ,116.72748]
yrange = [40.928879 ,41.528732]

plot, shape1[0,*],  shape1[1,*], xrange = xrange , yrange = yrange
oplot, shape2[0,*],  shape2[1,*]

shape3= shape_overlap (shape1, shape2, exists = exs)

print, exs

end

On 2月14日, 下午12时00分, "Weihua FANG" <weihua.f...@gmail.com> wrote: