[Al Skierkiewicz]

yash,
There are a number of calculations that need to be done once you have some known objects in the frame. If you are pointing the camera at a known object (size, shape and orientation in space) then you have to know the focal length of the visual field, how much the known object occupies and what orientation it might be in to make the calculations. In typical FIRST cameras, the focal length is known so there is no variable that has to be entered for zoom lenses and focus. In the cameras that are used for the virtual down line in football, there is sensors on the lens for focus and zoom, there are sensors for pan and tilt in the camera head and then there is positional info that supplied by the down marker flag. Each camera is calibrated for the field and there is obvious known size objects on the field so there is a lot of calculations done for that. Just to display the down line on program video, only three or four cameras are used and they require a 40' trailer of computers to make the calculations and supply the information to the computer that makes the display. If you watch, you will only see the line displayed on those cameras. Any of the other cameras will not show a down line and those are the dead give aways for the cameras that do not supply the info needed. Handheld and mobile cameras will never be the host camera for this display. with a fixed lense, and known size object you might be able to calculate distance if the object doesn't change aspect ratio with respect to the camera.