`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.