Patent ID: 7876361

Claim:
A method comprising: identifying a first line and a second line, substantially parallel to the first line, in a scene within a field of view of a camera; determining a distance between the first line and the second line, determining a first image-width of the first line, as the first line appears in an image of the scene, determining a second image-width of the second line, as the second line appears in the image of the scene, and determining a focal-distance of the camera from a plane that includes the first line and is substantially perpendicular to a center-line of view of the camera, based on the distance between the first line and the second line, and the first and second image-widths, wherein the first and second lines have substantially equal widths, and the focal-distance, d, is determined using: d=h*pw 2/( pw 2 −pw 1), where: h is the distance between the first and second lines, pw 1 is the image-width of the first line, and pw 2 is the image-width of the second line.