Syntax error Program to check given point in inside or boundary of given polygon or not in python

Program to check given point in inside or boundary of given polygon or not in python

Suppose we have a list of cartesian points [(x1, y1), (x2, y2), ..., (xn, yn)], that is representing a polygon, and also have two values x and y, we have to check whether (x, y) lies inside this polygon or on the boundary.

So, if the input is like points = [(0, 0), (1, 3), (4, 4), (6, 2), (4, 0)] pt = (3, 1)

then the output will be True

To solve this, we will follow these steps −

  • ans := False
  • for i in range 0 to size of polygon - 1, do
    • (x0, y0) := polygon[i]
    • (x1, y1) := polygon[(i + 1) mod size of polygon]
    • if pt[1] is not in range minimum of y0, y1 and maximum of y0, y1, then
      • go for next iteration
    • if pt[0] < minimum of x0 and x1, then
      • go for next iteration
    • cur_x := x0 if x0 is same as x1 otherwise x0 + (pt[1] - y0) *(x1 - x0) /(y1 - y0)
    • ans := ans XOR (1 when pt[0] > cur_x is true, otherwise 0)
  • return ans

Let us see the following implementation to get better understanding −

Example 

Live Demo

class Solution:
   def solve(self, polygon, pt):
      ans = False
      for i in range(len(polygon)):
         x0, y0 = polygon[i]
         x1, y1 = polygon[(i + 1) % len(polygon)]
         if not min(y0, y1) < pt[1] <= max(y0, y1):
            continue
         if pt[0] < min(x0, x1):
            continue
         cur_x = x0 if x0 == x1 else x0 + (pt[1] - y0) * (x1 - x0) / (y1 - y0)
         ans ^= pt[0] > cur_x
      return ans

ob = Solution()
points = [(0, 0), (1, 3), (4, 4), (6, 2), (4, 0)]
pt = (3, 1)
print(ob.solve(points, pt))

Input

[(0, 0), (1, 3), (4, 4), (6, 2), (4, 0)], (3, 1)

Output

True
Updated on: 2020-12-03T05:49:15+05:30

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