This is an interactive double leaf lift bridge based on the span over the Water of Leith
which was the seaport for Edingurg. It was built in 1830 and replaced by a more modern structure around 1912.
This is is designed to be triggered to open the span and stop automotive traffic when some form of water traffic
which has been set up as a locomotive comes within the trigger radius on the 4 invisible tracks in the water.
The blue invisible tracks is at ground level (z axis = 0 ft 0.0 in).
The green invisible track is at z axis = -10 meters (-32 ft 9.0 in) below ground level.
Water level should be set at -3 meters (-9 ft 10 in) below ground level.