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In October 2011, the PPMD specialized master's degree students (Photogrammetry, Positionning and Deformation Measurement) of the French ENSG (IGN’s School of Geomatics, the Ecole Nationale des Sciences Géographiques) were asked to come and survey the main facade of the cathedral of Amiens, which is very complex as far as size and decoration are concerned. Although it was first planned to use a lift truck for the image survey, budget considerations and taste for experimentation led the project to other perspectives: images shot from the ground level with a long focal camera will be combined to complementary images shot from what higher galleries are available on the main facade with a wide angle camera fixed on a horizontal 2.5 meter long pole. This heteroclite image survey is being processed by the PPMD master's degree students during this academic year. Among other type of products, 3D point clouds will be calculated on specific parts of the facade with both sources of images. If the proposed device and methodology to get full image coverage of the main facade happen to be fruitful, the image acquisition phase will be completed later by another team. This article focuses on the production of 3D point clouds with wide angle images on the rose of the main facade.

The transition from film imaging to digital imaging in photogrammetric data capture is opening interesting possibilities for photogrammetric processes. A great advantage of digital sensors is their radiometric potential. This article presents a state-of-the-art review on the radiometric aspects of digital photogrammetric images. The analysis is based on a literature research and a questionnaire submitted to various interest groups related to the photogrammetric process. An important contribution to this paper is a characterization of the photogrammetric image acquisition and image product generation systems. The questionnaire revealed many weaknesses in current processes, but the future prospects of radiometrically quantitative photogrammetry are promising.

Atmospheric haze variations, temporal differences, atmosphere’s or ground surfaces’ and Bidirectional Reflectance Distribution Function (BRDF), are well-known sources of radiometric heterogeneities in aerial images. It is necessary to correct them for many applications, such as the generation of large seamless mosaics of orthoimages, or land-cover classifications. This contribution describes a method for equalizing digital aerial images based on a parametric, semiempirical radiometric model. The model’s parameters are computed through a global least-squares minimization process, using radiometric tie-points in overlapping areas between images. The method may be called a “radiometric aerial triangulation” since its principle is quite similar to a standard aerial triangulation. It leads to a relative equalization between images, keeping their original contrast and color information. The method has been successfully applied operationally to more than forty projects comprising three to four thousands digital images each, for the creation of orthoimages over France. The results are good as long as atmospheric conditions are favorable and stable.

1. Cerema, Direction technique Eau mer et fleuves, Technopole Brest Iroise, 155, rue Pierre Bouguer, BP 5, 29280 Plouzane CEDEX, France. Amelie.Roche@cerema.fr 2. Cerema, Direction territoriale Sud-Ouest, Pole de competences et d’innovation applications satellitaires et telecommunications (PCI AST) Rue Pierre Ramond, CS 60013, 33166 Saint-Medard-en-Jalles CEDEX, France. Christelle.Bosc@cerema.fr ; Laure.Chandelier@cerema.fr ; Renaud.Lagnous@wanadoo.fr

This article presents the empirical research carried out in the context of the multi-site EuroSDR project "Radiometric aspects of digital photogrammetric images" and provides highlights of the results. The investigations have considered the vicarious radiometric and spatial resolution validation and calibration of the sensor system, radiometric processing of the image blocks either by performing relative radiometric block equalization or into absolutely reflectance calibrated products, and finally aspects of practical applications on NDVI layer generation and tree species classification. The data sets were provided by Leica Geosystems ADS40 and Intergraph DMC and the participants represented stakeholders in National Mapping Authorities, software development and research. The investigations proved the stability and quality of evaluated imaging systems with respect to radiometry and optical system. The first new-generation methods for reflectance calibration and equalization of photogrammetric image block data provided promising accuracy and were also functional from the productivity and usability points of view. The reflectance calibration methods provided up to 5% accuracy without any ground reference. Application oriented results indicated that automatic interpretation methods will benefit from the optimal use of radiometrically accurate multi-view photogrammetric imagery.