Question

I have a data-set that has four columns [X Y Z C]. I would like to find all the C values that are in a given sphere centered at [X, Y, Z] with a radius r. What is the best approach to address this problem? Should I use the clusterdata command?

Answer 1

Here is one solution that uses naively euclidean distance:

say V = [X Y Z C] is your dataset, Center = [x,y,z] is the center of the sphere, then

dist = bsxfun(@minus,V(:,1:3),Center);  % // finds the distance vectors 
                                        % // between the points and the center
dist = sum(dist.^2,2); % // evaluate the squares of the euclidean distances (scalars)
idx = (dist < r^2);    % // Find the indexes of the matching points

The good C values are

 good = V(idx,4);  % // here I kept just the C column