An image resection method applied to mapping techniques

Abstract

IZB n"72, 92322 Chatillon Cedex -France ADS T R ACTMapping techniques have emerged as reliahle measurement methods in a wide variety 0 1 fields. This is the case for temperature mapping aiicl flow field visualization. Another protiiising technique is pi-essure mapping based on pressure-sensitive paints.All these mapping methods provide images which ai-e very useful by thernselvcs because 2D o r 31) views allow improved knowledge about the studied behavior. The risefiilness of the image could further be enhanced by relating each imagc point to a point on tlic viewed object.A resection method is described. It allows data to he extracted from the iinagc and viitual images to be crcated. The method includes two parts. The first part covers recognition of' the camera location. The second part is the resection method itself. The hackprouric1 is clesci-ibetl and the software used is discussed. Finally three applications connected with teruperaturc mapping in wind tunnels illustrate the cap;ihility of tlie method.Mapping techniques are coirirnonly used in a wide variety of measurement applications. In aerodynamics they are irivolvccl in flow visualization and temperature measurement and arc becoming highly interesting for pressure nieasurement. Flow visualizations are commoiily made with laser systems providing a plane view. Thc images acquired can thereby hc related to the real 3D world without any major difficulty.Mapping temperature nicasiiremeiils are very usefui for heat rlux assessment in hypersonic ilows. 'These iiieasiii-etiic!its are inainly made by infrared thei-tiiography I 11\21. h i i t c;111 he made by phosphor thermography [31[4], liqliicl crystal thermography 151 and teinperature-sensitiv~ paints [61 [7]. The camera provides a picture fmrn a real 3D object. IJiifortunately the camera attitiidc arid location (hc,rcaftcrcalled CAL) are not well defined because of inaccurate CAL assecwicnt under wind tiiiine! conditions. The nroblcm arise.; 01 iinw ro process rhc irnnge 111 aim! !U i c i m ; I I I . :~ 1 x j t i i i to x i image point. l'ressure iiieasuremeiit with pressiirc-sensitive lurniiiescent paints (PSP) is a very promising mapping technique [8]/9].It is claimed that this technique can pr-wide an accut-acy of t11c same rnagnitude as with converitioiial equipincrrt. Tlierefore this niapping technique req~iircs ;in accurate riicthoti to estat,iisli the r-elatioiiship hetwcen the iinnge and the modci.The suhjcct of ohtaining information on the image and putting it on the real 3D model, called "resectim" i n this papcl-, has heen amply studied in computer vi:,ion and robotics. Brit only ;I few pt-actical applications have heen dcvclopctl for wind tunnel applic:itioiis [2]{9]. I t is assuitictl (hat (lie rcqiiit-et1 high accuracy, the pooi-illuniiilation quality and the iinfavorablc vicwiiig coiiclitioix ;ire significaii: rciisons foi-the 13ck o f i.csiil:\.[Iowevcr thc rniliii ireason is piohably due to tlie f x t that wiiicl tiiiiiiel nicasiirciiiciit teams :we not used io opcrnting iningin;: systcriis. ...

Infrared temperature measurements on 3D objects with surface recession

“…This object must be provided with detectable points, in order for them to be recognised in the thermal image. Two different techniques are reported in the literature: either the calibration points are embedded in the object of interest (in situ calibration), as it was proposed by Le Sant et al [5,6,7], or an external target, typically a planar surface, is exploited, as accurately described by Cardone et al [8]. In the former case, only a limited number of calibration spots can be placed on the test object, while in the latter case a pattern of equidistant points in two orthogonal directions is arranged on a calibration plate.…”

“…However, while infrared data are available in the form of 2D images, the observed test object surface is often non-planar and the precise spatial reconstruction of the temperature maps becomes a critical task. Optical calibration techniques have already been introduced in IR thermography by Le Sant [5,6,7] and Cardone et al [8]. These techniques adopt calibration targets or specifically designed control points on the investigated object, along with perspective projection models [9], to establish a relationship between the points of the observed surface and the image pixels, thus enabling the reconstruction of 3D temperature maps from the 2D thermal image.…”

Flow Visualization Measurement Techniques for High-Speed Transition Research in the Boeing/AFOSR Mach-6 Quiet Tunnel

“…The aligned images are then mapped onto the surface coordinates using resectioning methods. Various techniques are available here as well, such as the affine transformation [57], perspective and isometric projection [61], and the direct linear transformation (DLT) [56,62], which is a reduced form of the collinearity equations of photogrammetry. More sophisticated methods that involve techniques used for computer vision are also being developed, and the theoretical foundations for such techniques are discussed in Ref.…”

Photogrammetry Applied to Wind-Tunnel Testing

“…Photogrammetry is an important element of the data reduction process since TSP and PSP data in images must be mapped onto a model surface in 3D object space. Donovan et al [4], Bell and McLachlan [5], and Le Sant and Merienne [6] have described PSP mapping using photogrammetry. In applications of photogrammetry to TSP and PSP, the collinearity equations are used for mapping after the camera is calibrated.…”

“…However, photogrammetric techniques, while not in general widespread use in wind tunnel tests, have been used recently for luminescent paint and model deformation measurements. Donovan et al [4], Bell and McLachlan [5], and Le Sant and Merienne [6] have described the application of these methods to luminescent paint imaging. In addition, photogrammetric measurements of model deformation in wind tunnels have been reviewed by Burner et al [7] and Liu et al [8].…”