Problem with shapely polygon contain, seems not to correctly flag all contained points

Question

Lets say we have a 100x100 grid that contains a polygon. Now if we color all possible (x,y) points [x,y are integers] that are contained in the polygon we should expect the polygon to be somewhat painted/filled

But the image that i'm getting never properly falls within and fills the polygon! Is this a limitation of shapely or am I doing something wrong?! (please note I need this to work for other purposes and not just paiting a polygon)

polygon and filled area not overlapping

import numpy as np
import matplotlib.pyplot as plt
import shapely.geometry

points = np.random.randint(0,100, (10,2)) # 10 random points
poly   = shapely.geometry.MultiPoint(points).convex_hull.buffer(1) # a polygon 
grid_points = [ shapely.geometry.Point(x,y) for x in range(100) for y in range(100)]
in_poly = np.array([poly.contains(point) for point in grid_points])

#plot
plt.imshow(in_poly.reshape(100,100), origin='lower')
plt.plot(*poly.exterior.xy)

Answer 1

This seems to do what you want - replace this one line (swap y and x in for loops):

grid_points = [ shapely.geometry.Point(x,y) for y in range(100) for x in range(100)]

---

Couple of notes:

My installation of shapely has this module name (geometry spelled differently so you may need to change name in above line):

  import shapely.geometry

And thanks for adding the second plot command - that helped a bunch.

Something along the way has differing major orders (row-vs-column) so the above line changes to column-major.

And it may be you'd want to compensate by doing the inverse on the exterior plot.

(original (with new random shape), updated, with exterior)