Precise center location for light spot contour images of light emitting diode control points in light-pen vision coordinate measurement

In a light-pen single-camera three-dimensional (3-D) coordinate vision measurement system, a key step is the fast and precise center location for the light spot contour images of the LED control points obtained by the charge-coupled device (CCD) camera. A novel center location scheme for the light spot contour images is proposed in this key step. This scheme uses a geodesic active contour model to obtain every light spot's contour edge simultaneously. Then the center coordinate of every light spot is measured using a subpixel scheme. Compared to the common scheme using the edge detection and the contour tracking, this scheme is highly precise and fast for the center location of every light spot in a CCD image.