    vel.findIntersection(ref, target)

Find the intersection of a line starting in the center of the SVG node ending in the point `ref` (an object of the form `{ x: Number, y: Number }`). `target` is an SVG element to which this node's transformations are relative to. In JointJS, `target` is usually the `paper.viewport` SVG group element. Note that `ref` point must be in the coordinate system of the `target` for this function to work properly. This function returns a point in the `target` coordinte system (the same system as `ref` is in) if an intersection is found. Returns `undefined` otherwise.