Experimental Validation of Close-Range Photogrammetric Measurement Performance of Doubly Curved Surfaces

*† ‡ , In this paper, we review the results of rigorously quantifying the noise floor of projected dot photogrammetry as it applies to the measurement of doubly curved surfaces, membrane optical shells in particular. To this end, a series of calibration artifacts were manufactured, characterized with CMM, and then characterized with projected dot photogrammetry. This was done for both a 0.2 and 0.5m shell characterization hardware configuration for with R#’s of 1 and 0.75 respectively. R#’s were chosen to match the shape of typically tested membrane shells. A summary of test methods, post processing steps, and typical results are reviewed. Target sample spatial sampling frequencies of 6 to 11 mm are regularly attainable. Non rigid body noise floor is shown to be approximately 2 to 3 um rms over a 0.5m test object and 1 um rms over a 0.2m test object, or approximately than 200,000:1. Better results are attained on a 0.2m test set up due to a combination of better use of image space, improved dot planarity and depth of focus, etc. Experimental repeatability is accessed, both for the calibration artifact, and representative shells and shown to be quite good. Studies of the effect of # of imagers and # of targets on solution are also reviewed. In general, projected dot photogrammetry is shown to be quite repeatable and capable of making high accuracy measurements of global figure errors. Given these results, it is felt that the projected dot photogrammetry measurement technique is extendable to a wide range of surface shapes and possible use as deployment monitoring and/or initial surface phasing sensor.