calcpos.m

function [xy, q, s] = calcpos(abcd, Kx, Ky, Ks)

if nargin < 2
    Kx = 1;
end
if nargin < 3
    Ky = 1;
end
if nargin < 4
    Ks = 1;
end

a = abcd(:,1);
b = abcd(:,2);
c = abcd(:,3);
d = abcd(:,4);

ac = a-c;
bd = b-d;
ab = a-b;
cd = c-d;
sum = a+b+c+d;

xy = [(ac-bd)./sum*Kx (ac+bd)./sum*Ky];
q = (ab+cd)./sum*Kx;
s = sum*Ks;