Loop Measurement in a dimension

[#1]

We can measure the loop length of a spline or 3D path with the measurement tool, but no way to put that in a dimension. Many times we need to route a wire of a specific length and must set loops or curves to take up the slack.  It's very tedious to adjust some parameter and go back to the 3D sketch to measure the loop length.

If this could be done it would also be useful to be able to constrain the length of a spline (so we could tie the endpoints, set the length and adjust the path to accomodate).