True length of a segment

Find the true length of segment AB, with A(12, 2, 7) and B(40, 16, 7).

Step-by-step solution

Choose a plane containing AB and perpendicular to the PH: its horizontal trace is the hinge.
Rotate A and B onto the PH around that hinge.
The distance between (A) and (B) is the true length of AB.
Check the result with d = √(ΔX² + ΔY² + ΔZ²).

Result: 31.3 units.

If the segment is parallel to the PH it is already in true length in the plan; if vertical, in the elevation.