Laser Measurement and Reconstruction of Curved Plates
An automated system has been developed which acquires range image data from a curved plate, analyzes them and yields a suitable mathematical representation. The plate is assumed to be topologically equivalent to a four sided free-form surface representable in an explicit, non-parametric form, whose tangent values in every direction are small. The system consists of three parts: a laser scanner, a robot and a workstation. Each system is connected through TCP/IP and a serial line so that all operations are synchronized. The limitation of the scanner that the size of the rectangular array of points produced by the scanner is too small to capture the whole shape is avoided by attaching the scanner to the robot so that enough shots to cover the whole object can be taken by placing the scanner at appropriate positions. The procedure starts with detecting roughly the edges of the plate, which is necessary to compute the number and poition of the shots that are needed to obtain the full model. Edges are detected by investigating changes of tangent values along each raster line of the scanner. The rough estimation of boundary is followed by scanning of the plate that starts from a corner and sweep through the whole plate in a zig-zag manner. Registration technique is used to accomplish the congruence of geometric representation of the model with a set of arrays of points. Data points sampled along raster lines of digitized points are approximated by B-spline curves, which are lofted in the least squares approximation scheme so that the B-spline surface approximating the plate is obtained. Examples are given and comparison between the measured data from the plate and the B-spline surface representation is made.
Computer Program showing a surface of a plate
Surface Construction from Scanned Data
