Sorting coordinates on radial distance from origin

Very new to MatLab and struggling with what I think is probably very easy.

I have a set of x,y coordinates over time from particle tracking analysis. I would like to set the origin to a specific x,y coordinate and then calculate the number of coordinates that are some given radial distance from this origin.

Any help greatly appreciated!

Answer 1

[Torsten]

If (x0,y0) is the reference point and your coordinates are saved in a matrix XY of size (2xn), then just use

R = 2.0;   %e.g.
n = numel(find((XY(1,:)-x0).^2+(XY(2,:)-y0).^2 <= R^2))

n is the number of points in the XY matrix that lie within a radial distance of R from (x0,y0).

[James Tursa]

Or just replace numel(find(... with sum(... or nnz(...

[George Vaisey]

Worked great, cheers!

Answer 2

[Matt J]

Here's one way to do that:

[~,distance] = cart2pol(x-x0,y-y0);  %distances from (x0,y0)

count = nnz(dist_Lower<=distance & distance<=dist_Upper) % count the number within a certain distance range