PHOTOGRAMMETRIC MEASUREMENT OF LINEAR OBJECTS WITH CCD CAMERAS - SUPER-ELASTIC WIRES IN ORTHODONTICS AS AN EXAMPLE

摘要

This paper describes the development of an approach for nearly automatic recognition of the shape of linear objects on the example of super-elastic wires in orthodontics. This is made possible by the integration of known parameters which describe the general shape of the objects concerned. Such parameters are derived from the production process of these objects. A digital photogrammetric 3D measurement system should give a touchless measurement of the wires. The images were taken with two CCD cameras. The goal was to find specific algorithms for object recognition and to apply them to the measurement of the wires. The algorithm should guarantee an automatic extraction of edges of a linear object by model based procedures in the image. In this case, a 3D model should be derived from the parameters controlling the production process. It should be introduced into the algorithm as a base of knowledge. As a result we get new 3D coordinates of the vertices of the wires. The edge lengths and the bending and torsion angles between the vertices could be derived from these coordinates. Afterwards the results were compared with the parameters of the bending machine, and the accuracy of the photogrammetric procedure was evaluated.