Stereoscopic rangefinder

One of the projects I was mulling on before was a stereo rangefinder using two PTZ cameras.  The concept is simple, when an object is being viewed by two cameras, its distance can easily be calculated.  Since the distance between two PTZ cameras is known, the distance of the object can be derived trigonometrically.  This concept is still being used by existing optical rangefinders despite the presence of accurate laser rangefinders.

During World War II, Allied and German tanks slaved their optical rangefinders to the tank main gun.  To operate these rangfinders, the gunner needs to merge the two views into one object and the gun automatically is set to fire in the predetermined range.  To illustrate:

sin B=b/c

c= b/sin B

  c^2   =   a^2 + b^2 

      

  a=  sqrt (c^2 - b^2)

Reference to such system is shown below:

"Using stereoscopic images to determine the range to objects isn't a new phenomena. Before the age of the laser manual stereo correspondence was used on ships and also amusingly on battle tanks. This web page describes the use of a stereo range finder in an M48 Patton tank as follows:

When first deployed, the M48-A3 had for the 1960s a state-of-the-art fire control system. At the time computers were mechanical, and range to the target was provided by a stereoscopic range finder, which functioned similarly to a 35mm camera. An end-box on each side of the turret exterior held a prism-type mirror. Turning a hand-crank on the range finder would pivot these mirrors until the double-image in the range finder merged. As the distance between the mirrors is exactly known, a little trigonometry provided the range (in meters) to the target. This information was displayed on a range indicator, and also fed to the ballistic computer by a rotating shaft. The ballistic computer was a collection of gears and cams--nothing was solid-state--which had a handle so that the gunner could select the type of ammunition that was to be fired. Each round had a different muzzle velocity, and therefore the computer had a different cam for each type. The computer would take the range data, merge it with the velocity data, and via a set of rotating shafts, supply this information to the gun's super-elevation mechanism, resulting in the gun being elevated above the gunners line of sight sufficiently for the round to overcome the downward pull of gravity on its way to the target.

The stereo range finder was effectively a dual lateral periscope, with the sights protruding from either side of the metallic monster as shown below. Using the stereo ranger was referred to as "flying the geese" due to the appearance of the markings which needed to be optically aligned."

With the advent of computers and video intelligence, the process of aligning the images and getting the range of a certain object can be automated and derived with ease.  Practical applications for such a system is however limited.