IMAGE REGISTRATION FOR PRESSURE-SENSITIVE PAINT APPLICATIONS

Pressure-sensitive paint (PSP) data are generally derived by ratioing two images of a PSP-coated wind tunnel model. One image is taken at a known ''wind-off'' reference pressure while the other is taken at the test condition, in order to factor out the effects of nonuniform illum ination and paint thickness. However, airloads on the model cause it t o move during testing with respect to both the camera and the illumina tion source used to excite the PSP. Thus, the raw PSP images must be a ligned, or registered, by means of a spatial transform. Once a proper ratioed image is obtained, image coordinates must be related to model coordinates so that pressure data can be obtained at the desired point s on the model. This article compares several transforms used for imag e registration, and demonstrates the use of the projective equation of photogrammetry to relate model to image coordinates. An application i n a small-scale wind tunnel test is shown, demonstrating mapping of pr essure data to the three-dimensional model surface.