Generate random polygons within another polygon using shapely in python

Question

I have a use case where given a polygon on the US map, I need to generate n rectangles within the polygon defined on the US map. I have been trying stuff with shapely, but stuck.

So the code would work in this way.

1. Define the upper level polygon

poly = Polygon([(-123.52380921651545,44.92842807389871), (-115.78943421651545,32.651610397456906),(-81.95154359151545,33.71815014381751),(-78.74353577901545,39.29454038362893),(-91.57556702901545,42.223006851069464),(-106.29724671651545,45.207760924293545),(-123.52380921651545,44.92842807389871)])

2. Write function which takes polygon defined in step 1, and number of rectangles that need to be created within that polygon.

def random_polygon (poly, num_polygons, points_per_poly=4):
    min_x, min_y, max_x, max_y = poly.bounds
    random_poly = []
    while len(random_poly) < num_polygons:

3. What is the syntax in this piece, where I generate a random rectangle, where the length and breadth is fixed, but the co-ordinates are different for each rectangle. Once the rectangle is generated I check if it is within bounds of polygon created in Step 1. If yes I add it to random_poly and continue.

Answer 1

Steps:

1. Define a random point for each axis within the bounds.
2. Assume that to be top-left point and create a rectangle.
3. check if that rectangle is within the outer polygon

import random

from shapely.geometry import Polygon, Point
poly = Polygon([(-123.52380921651545,44.92842807389871), (-115.78943421651545,32.651610397456906),(-81.95154359151545,33.71815014381751),(-78.74353577901545,39.29454038362893),(-91.57556702901545,42.223006851069464),(-106.29724671651545,45.207760924293545),(-123.52380921651545,44.92842807389871)])

min_x, min_y, max_x, max_y = poly.bounds

width = # to be defined
height = # to be defined
num_polygons = # to be defined
random_poly = []

while len(random_poly) < num_polygons:
  rand_x = random.uniform(min_x, max_x)
  rand_y = random.uniform(min_y, max_y)

  left = Point([rand_x, rand_y])
  bottom = Point([rand_x, rand_y - height])
  right = Point([rand_x + width, rand_y - height])
  top = Point([rand_x + width, rand_y])

  new_poly = Polygon([left, bottom, right, top])

  if poly.contains(new_poly):
    random_poly.append(new_poly)