Determining if points lie within a sphere

I have a set of points P(x,y,z) and a sphere defined by its centre (x0,y0,z0) and radius r. I want to find the points that lie within or on the edge of sphere. I can run a loop for all points and check the condition:

(x-x0)^2+(y-y0)^2+(z-z0)^2<=r^2

But, Is there a direct function or any cheap method that would directly give me the indices of all points that lie within the sphere? Something I can easily use when there are large number of points and different sphere radius to test?

Thank you.

Answer 1

[Matt J]

Do you really need the indices? You can readily obtain a logical mask of the points in the sphere with,

mask = (x-x0).^2+(y-y0).^2+(z-z0).^2<=r^2;

If you really do need the indices, then,

find(mask)

[Vinit Nagda]

Thanks for your response.

Yes, I need the indices. Each point carries some weight. I have to evaluate the mean of the weights of points that lie within the sphere.

[Matt J]

OK, but I showed you how to get the indices, so you have your answer. Please Accept-click the answer then, unless there is some unresolved issue.

[Matt J]

Yes, I need the indices. Each point carries some weight. I have to evaluate the mean of the weights of points that lie within the sphere.

Incidentally, that doesn't explain why you need the indices. You could instead just do,

mean(weightVector(mask))