System alignment strategies impact the overall performance of white light scanners, in particular affecting the
uncertainty that is determined using the sphere spacing error specified in the VDI 2634 guideline. This paper addresses
the accuracy of optical white light or so called "topometric" scanners. In almost any application of such scanners it is
necessary to put together scans from different directions: from a couple of scans to a couple of hundred scans. Accuracy
for the scanner itself can usually be well described for a single scan. However, the accuracy for assembled data sets
from many scans is harder to estimate and specify as it depends on many more parameters as well as on the alignment
strategy being used. This paper will describe different alignment strategies including the use of robots, tracking systems,
and targets, as well as best fitting methods. The impact of these methods on the resulting overall accuracy is described
and demonstrated using real test examples. In addition, different methods of achieving these accuracy numbers will be
presented including using guidelines such as provided in VDI 2634. This paper will briefly touch on the basic principles
of white light scanning to understand the potential as well as to illustrate the limitations of these techniques.
This paper is intended to provide a useful guideline for engineers or quality managers who want to establish or learn
more about new scanning technologies, with special attention given to the accuracy issues.
Three-dimensional-metrology based on photogrammetric and topometric techniques is a powerful tool for the digitization and measurement of complex three-dimensional scenes and objects. Since several years advanced sensors and measurement systems are available for industrial applications. Especially the integration of topometric systems into measuring- and handling machines is supported by compact and light 3D- sensors. These sensors can be optimized for specific measuring tasks with respect to accuracy, field of view and further parameters. During the last two years one is going to describe both techniques by the same algorithms. Moreover, there are first approaches of 'topogrammetric' systems, that combine photogrammetric and topometric metrologies, especially by using calibration techniques that are well known in photogrammetry and which allow the on-line calibration of 3D- sensors. On the other hand the topometric projection of coded light provides a continuous indexing of the whole measuring scene where photogrammetric methods (without active illumination) are limited to a lower number of discrete index marks.
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