If you are doing a single photo project that uses Edges and Constraints, and after processing the 3D Viewer shows only one Edge, then you have not set up enough Constraints.
The Single Photo algorithm will arbitrarily pick a point to be called the origin (0,0,0). It then propagates the information along constrained objects (given the computed camera station and photograph marking data). Since Edges do not connect to other objects (unlike Lines which connect at Points) the only way to propagate information from them is to put them in a Surface Constraint.
Adding an Axis Plane Constraint, placing the desired Edges in that constraint and then processing will fix the problem.