High precision photogrammetry is an appropriate tool to measure coordinates of concen­trator support points and mirror surfaces, especially for the analysis of large concentrators. The photogrammetric method directly delivers coordinates of selected test points and thus allows geometrical assessments of the concentrator. Previous work has described the ap­plication of photogrammetry to the characterization of solar collectors [1]. Close-range photogrammetry involves the use of a network of multiple photographs of a targeted object taken from a range of viewing positions, to obtain high-accuracy, 3-dimensional coordinate data for the object being measured. A significant advantage of photogrammetry is that it is a rapid non-contact technique that can readily be applied to many kinds of measuring ob­jects. With appropriate retro-reflective targets and flashlight it can be performed during the
day, even under bright sun. After application of the targets, actual measurement time for a set of 10 to 30 photos is short. Until now the techniques have been applied on R&D level to measure the collector assembly jig and EuroTrough collector modules.

The collector assembly jig is an essential part for the precise assembly of EuroTrough space frames. Therefore it needs to be rigid and all support points well adjusted. Photo — grammetry has been used to test the jig setup. Figure 1 demonstrates the photographing with a 5m tripod and the resulting camera positions.

The results have been compared to results obtained from conventional measurement and levelling techniques and have demonstrated the advantage of photogrammetry in 3­dimensional measurements. For manufacturing quality control photogrammetry will always have to be combined with the other techniques.

The assembly of the collector modules is done on these kinds of jigs. Checking of the as­sembled steel structures can be performed very well with photogrammetry. Figure 2 shows the space frame of a 12 m long collector module prepared for the check. Retro-reflective targets are placed on all 112 of the mirror support points. The colour graph on the right side of Figure 2 represents a measurement result.

A typical quality control plan will include such measurements with a decreasing sample testing rate over the duration of the construction phase. Typically statistical information is
gathered from the measurements such as drifts and outliers in order to produce constant assembly quality.

The final result of the assembly process after absorber mounting might be affected by the intermediate assembly steps. This is why a final inspection of the collector geometry should be introduced in certain intervals. For final checking targets are attached onto the mirror surface for the photogrammetry and can be removed easily after the measurement (Figure 3, Figure 4). The results of such measurements on EuroTrough collectors proved the excellent quality of the assembly procedures in terms of geometric accuracy.

A typical configuration for a photogrammetry system for quality control consists of a fix frame of several digital cameras and flashes, which transmit the captured images directly to the evaluation computer system. The fix set-up in a workshop reduces the effort for the photogrammetry evaluation, so that the results can be obtained from automated software in very short response time and with constant accuracy.