mainly consists of a specially designed light
pen, one or more high-resolution CCD cameras (Only one is
used in our current design) and a laptop computer. On the light
pen there are at least three point shaped light sources (LEDs)
and a touch trigger probe with a spherical stylus. Three light
sources and the probe stylus must be aligned in one line with
known positions. During measurement the touch trigger probe
contacts the object surface to be measured and the image of the
light sources on light pen is captured by the CCD camera. The
image is processed by the computer and 3D coordinates of the
contact point can be calculated with a predefined algorithm. In
this way, coordinates of all points are sampled in turn. The
geometrical features such as the dimensions, forms and
position errors of the objects are evaluated by the software
package based on the obtained 3D coordinates.