Abstract: Techniques pertaining to methods and devices for calibrating camera parameters are disclosed. According to one aspect of the present invention, objects on an image are detected and features on the objects, such as the top of a person, are identified. Perspective parallel lines based on the object features are constructed and vanishing points from the converged perspective parallel lines are determined. A vanishing line is defined according to the vanishing points. The intrinsic parameters, such as focal length, and the extrinsic parameters, such as tilting and pan angles, of a camera are calibrated according to the vanishing points, the vanishing line and a reference object with known dimensions, or known camera angles, The calibrated camera parameters are used for accurate photogrammetric measurements and computer vision applications.

Abstract: Techniques for synchronizing clocks are disclosed. According to one aspect of the present invention, a pair of dividing coefficients a1 and a2 is obtained from a ratio of a theoretical frequency fs1 of the first source signal to a theoretical frequency fs_local of a desired local clock signal. A least common multiple expressed as T_c is obtained from the theoretical periods T1 and T2 of the first source signal and the second source signal. A relative error expressed as k is calculated from the first and second source clock signals in a period of T_c. The first source clock signal is then divided into a first local clock signal with a period equal to T1*a1 and a second local clock signal with a period equals to T1*a2 according to the dividing coefficients a1 and a2, respectively. The clock number m of the first local clock signal and the clock number n of the second local clock signal in the period of T_c are calculated according to the relative error k and the dividing coefficients a1 and a2.