Javascript function to return post-transform coordinates of an element.

post-transform-coords.js

// Return the post-transform coords of an element,
// assuming that proper pre-transform coords are supplied.
function getElementCoords(element, coords) {
    var ctm = element.getCTM(),
    xn = ctm.e + coords.x*ctm.a,
    yn = ctm.f + coords.y*ctm.d;
    return { x: xn, y: yn };
};

var circle = document.getElementById('svgCircle'),
x = +circle.getAttribute('cx'),
y = +circle.getAttribute('cy'),
coords = getElementCoords(circle, {x:x, y:y}); // Any object with x,y properties will do.

// An alternate method that takes translate and scale
// parameters to accomplish the same task.
function getScreenCoords(x, y, translate, scale) {
    var xn = translate[0] + x*scale;
    var yn = translate[1] + y*scale;
    return { x: xn, y: yn };
}