How to delete a set of meshgrid points inside a circle?

Question

I am trying to create a meshgrid without some of the points that falls within the circle having specified coordinates and a radius. I am not able to subtract the grid points

Answer 1

You cannot remove the points within the arrays x and y. It is a 2D problem and the values that need to be removed from x depend on y and inversely.

What you can do is operate directly on the mesh you created (X and Y). For example,

import math
import numpy 
import matplotlib.pyplot as plt


N = 200
x_start, x_end = -2.0, 2.0 
y_start, y_end = -2.0, 2.0


x = numpy.linspace(x_start, x_end, N)
y = numpy.linspace(y_start, y_end, N)

circle_x, circle_y, r= 0.0, 0.0, 0.4

X, Y = numpy.meshgrid(x, y)

## Define points within circle
pts = (X-circle_x)**2+(Y-circle_y)**2 <= r**2

## Create a constant mask over grid
M = numpy.ones(X.shape)
## Assign 0 to mask for all points within circle
M[pts] = 0

size = 10
fig = plt.figure()
plt.imshow(M)
plt.show()

This does not remove any points from X or Y. If instead, you wish to only perform calculations on part of the points, you could do

pts = (X-circle_x)**2+(Y-circle_y)**2 > r**2
X = X[pts]
Y = Y[pts]

plt.scatter(X,Y)
plt.show()