getCTM失败坐标

Question

为什么使用矩阵setCTM会导致坐标的减少和移动？如何获得坐标是准确的？ http://codepen.io/anon/pen/mVGgVq

function btncircles(e) {
  var node = e.target;  
  var x = node.getAttribute("transform");
  var ctm = node.getCTM();
  var transform = document.createElementNS(svgns, "svg").createSVGTransform();
  var matrix = document.createElementNS(svgns, "svg").createSVGMatrix();
  var sa = ctm.a;
  var sd = ctm.d;
  matrix.a = sa;
  matrix.d = sd ;
  matrix.e = ctm.e;
  matrix.f = ctm.f;
  transform.setMatrix(matrix);
  node.transform.baseVal.initialize(transform);
}