Details

In a pinhole camera, light enters the camera through a tiny hole and illuminates the image plane. A pinhole camera has a focal length , the distance from the pinhole to the image plane. The pinhole is shown with a blue point and the image plane as a blue line. 3D points in the camera's coordinate frame are converted to image plane coordinates according to the formula:

, where .

All lines parallel to the camera frame's axis terminate at at the vanishing point in the image plane.

Lasers mounted at and that terminate at coordinates and have image plane coordinates and .

Thus the distance to objects with image plane coordinates and gives camera frame coordinates and .

If both lasers strike the same object, the angle to the object is computed as .

A camera's reticule (or graticule) is a net of fine lines in the scope. In this case, the reticule is aligned with the vanishing point of the lasers. The readings on the reticule directly measure the distance from the object to the camera.