3D view of a PSP test made on
a 206 PSA model (PSA/ONERA cooperation)
Big size: 91 Ko
avi movie (1 Mo)
Optical mapping methods are often used for wind tunnel testing, as heat flux measurements with infrared thermography (see French pages) and pressure measurements by using PSP (Pressure Sensitive Paint). These measurement methods provide quantitative images, which are really useful only when the location of the model has been recognized in them.
Among the optical methods, PSP has been the one that has required sophisticated image processing tools. These tools are gathered into softwares called resection softwares. They differ from usual image processing softwares by the following features:
They provide a sub-pixel accuracy in order to extract accurately the relevant information from the images.
Markers are used to identify the relative position of the model and the camera. The contours of the model are not used because they are blurred or not in the image.
The mathematical operations done with the images are performed with a sub-pixel accuracy.
The actions can be automated enabling to process the images in near real time.
The resection software AFIX2 has been developed at the division DAFE. It is used in the Onera's industrial wind tunnel division to handle PSP and IR tests. It is distributed as a freeware. A full example is provided in this site. AFIX2 is not used only for PSP and IR applications. It can be used for conventional image processing applications, as for vortex tracking in images delivered by laser sheet methods. It can also be used to measure model deformations.
image processing: enhancement, filtering (median, smoothing, gradient, curvature, histogram equalization, etc…), thresholding, mathematical opérations, mask, extracting information, camera calibration, etc.
markers: automatic recognition, management, automatic linking with real markers (3D matching), cleaning, etc.
resection: grid management, automatic identification of camera parameters (rotations and distances), extracting information, creating virtual images, integration, model deformation correction, model deformation measurement, stereoscopic applications, etc.
self-illumination effect (not available in the standard version, contact "lesant @ onera.fr"): image segmentation, lambertian or real BRDF, image correction.
calibration: PSP calibration with 1, 2 or 3 images (for usual paints or binary paints), TSP calibration with 1, 2 - or 2 images, IR calibration, mask or pixel by pixel calibration, a priori calibration, in situ calibration, applying the calibration to convert the image in a quantitative image (pressure or temperature).
tools: converting image coordinates in world coordinates, films, renaming files, etc.
macro system: The commands are saved in macro files, which in turn can be edited (with txt editors) and optimized. A number of functions are available: variables, tests, loops, calling other macros, interacting with the user, automated data reduction, etc. The macro system can be used to remote applications on Excel or Tecplot to fully automate the data reduction process.
Publications
The following example is given to highlight the most important features of AFIX2.
Le Sant, Y., Deléglise, B., Mébarki, Y, "An Automatic Image Alignment Method Applied to Pressure Sensitive Paint Measurements", 1997, 17th ICIASF, Monterey (U.S.A.), September 29, October 2. PDF(994K)
Le Sant, Y.," Image processing tools applied to wind tunnel testing", 48th CASI Annual Conference, Toronto, Canada, 29 avril - 2 mai 2001. PDF(1915k)
Le Sant, Y. et Mérienne, M.-C., "Mesure de la pression pariétale à l'aide de peintures sensibles à la pression". 9ème Colloque Francophone de VISUalisation et de traitement d'images en mécanique des FLUIdes, Rouen, France, 18-21 juin 2001. PDF(1237K)
Le Sant, Y., "Overview of the self illumination effect applied to Pressure Sensitive Paint applications". 19th ICIASF, Cleveland, OH, August 27-30, 2001. PDF(1134K)
