Dimension to center between two references

[gustavb87]

I would like to be able to place a dimension at the center point or center line between two other references. This is currently only possible on family instances with a defined center reference plane or system families with a defined center line. It would be very nice to be able to dimension to center on DirectShape geometry and other geometric elements by just selecting the two references I want the center point/line between. It would also work on circular geometry by getting the point directly in the middle between the two widest points on the circle, which we today are able to snap to. This would be very helpful on CAD/IFC links and Data Exchange Elements that do not have defined references for their centers. It would also make it easier to dimension to center in 3D views. 

I think this can be done either with a new Dimension Type in the Annotations Panel or with a new option under "Edit Witness Lines" when editing a Linear dimension already placed.