The monitoring system uses a basic triangle. Two cameras (camcorders) are placed on opposite sides of the airplane's approach to form the base of the triangle. The airplane creates the third point of the triangle. The cameras are fixed in position and by knowing the tilt of the cameras you can determine the height of the aircraft.

The altitude formula (above) requires the distance between the two sites (base-length) and the two elevation angles from the cameras to the aircraft. This formula gives the aircraft's height above the site. To calculate the aircraft's Mean Sea Level (MSL) altitude you would add the site's MSL altitude to the height of the aircraft above Site A.

If the sites are at different altitudes from each other then the base-length has to be modified to make the formula work correctly. The modified-base-length= base-length + (altitude Site B - altitude Site A)/TAN (angle B). For this to work, just remember to make Site B the site which is higher in altitude.

The distance along the ground from Site A to directly under the aircraft= (aircraft height above Site A)/ TAN (angle A).