function f = cofmass3d(mat3D)
%computes the centre of mass in a 3D volume

%determine the size of the matrix
dimensions=size(mat3D);
rows=dimensions(1,1);
cols=dimensions(1,2);
plan=dimensions(1,3);
npoints=sum(sum(sum(mat3D)));

%calculate the centre of mass for the x co-ordinates
x = 1:rows;
  y = 1:cols;
    z = 1:plan;
        rowtotal=sum(x*mat3D(:,y,z));
        coltotal=sum(mat3D(x,:,z)*y');
        platotal=sum(mat3D(x,y,:)*z');

f=[rowtotal/npoints coltotal/npoints platotal/npoints];