Projectile velocity and spin rate by image processing of synchro-ballistic photography

Digital image processing has been used to measure projectile velocity and spin rate from pairs of synchro-ballistic camera images. Two cameras displaced along the flight path are used. Each image contains the projectile image and timing marks to determine the time scale. Both cameras use the same timing generator allowing a common timing mark denoting the same instant to be defined in both images. Velocity is determined from the actual projectile length the length in the image and the time scale. A circumferential sawtooth pattern painted on the projectile is used to determine the rotation angle in each of the two images. The distance between the common timing mark and the. projectile tip is used to determine the time at which the projectile passes each camera. The spin rate is computed as the angle difference divided by the time difference. The user interface is organized as a computer spreadsheet input values may be entered in any order. The operator recognizes the key points in the image and digitizes their coordinates using an operator-controlled trackball. Interactive contrast enhancement image scrolling and zoom are provided. The measurement accuracy is comparable to manual methods but the time required is significantly reduced.