A measurer sent me his cal course map with the endpoints defined by straight line distances from 2 fixed objects on the side of the road. For example he measured from his PK nail to a lamppost just south of the nail, and to a lamppost just north of the nail. He didn't measure the distance along the direction of the road, but straight to the lamppost. A person trying to locate the nail (or where the nail used to be) would need to find the intersection of the arcs.
When there are no landmarks actually on the road, this seems to me like a much more precise way of defining the endpoint location than giving the distance in a direction along the road.