Railroad Surface Inspection
Rail gage is the measurement between the inner surfaces of the rail tracks. This distance is critical for safe operation of a locomotive on the tracks. This inspection algorithm measures the gage from a drone flying at 250 ft above the track with a zoom lens and accurate telemetry data.
The gage is independently calculated every few inches using photogrammetric techniques. The measurments are heavily filtered to reduce noise and can provide accuracy of about 1/8".
Note: Yes, it is really spelled "gage" when dealing with railroad tracks...
Rail Gage Inspection Examples