Image Processing Tools Used for PSP and Model Deformation Measurements

Abstract

Recent advances in using image processing tools for wind tunnel applications as PSP (Pressure Sensitive Paint) and model deformation measurements are presented. The input for these tools is markers located on the model as well as on the wind tunnel walls. Assessing their image coordinates is then the first step of the image processing pipe. A dedicated tool has been developed and its accuracy is discussed in detail. Then the matching step with real markers known by their world coordinates is presented. The algorithm is quite new and uses the RANSAC paradigm. It is 3D and models the l ens with the usual pinhole lens model. As a result, it solves also the camera pose problem together with the matching problem. Finally, model deformation can be assessed with a grid tracking method, which enables to measure 3D deformation even with only on e camera. It has been learned from a lot of PSP tests that the residual error comes uncertainties about marker world coordinates as well as from optical distortions. A new approach has been developed to calibrate the camera parameters and to measure the ma rker coordinates by using several views of the model in the test section. This method is simple and provides a high accuracy. Determining model deformation requires an accurate in situ camera calibration which is still a problem in wind tunnel testing. A s olution is proposed which used the epipolar geometry which solves the matching problem even for unknown markers.