| Residing on a SUN SPARC station with an ANDROX image board and two CCD cameras, a digital photogrammetric system, STEREO, is implemented with approximately 13,000 lines of C code to determine three dimensional coordinates of points of interest (POI) defined with a grid on a texture-less smooth specimen. Two CCD cameras were set up with unknown orientation and took digital images of a model and the specimen. Points on the model were selected as control or check points for calibrating or assessing the system. With a new algorithm for edge-detection called local maximum convolution (LMC), the POIs were extracted from the stereo image pairs and matched automatically. Based on the result of image matching, the image coordinates of the POI's, together with the image (and object) coordinates of the check (and control) points, are directly imported into a least squares "bundle" adjustment procedure. This procedure solves for the camera orientation parameters, the object coordinates of the POIs and the object coordinates of the check and the control points. By comparing the known and the computed object coordinates of the check points, the standard deviation of the residuals at the check points was approximately 24%, 49% and 56% of the pixel size in the X, Y and Z directions, respectively. The average of the absolute values of the residuals at the check points was approximately 19%, 36% and 49% of the pixel size in the X, Y and Z directions, respectively. With the graphical user interface, STEREO demonstrated a high degree of automation and its operation does not require special knowledge of photogrammetry, computers or image processing. |
