Numérisation 3D in situ du squelette d’Australopithèque «Little Foot» à Sterkfontein, Afrique du Sud

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Dans cet article, nous décrivons la méthodologie développée pour numériser un site de fouilles d’un très ancien fossile d’homininé (StW 573, Little Foot), découvert dans les grottes de Sterkfontein, en Afrique du Sud. Nous détaillons les aspects pratiques d’acquisition de vues 3D avec deux scanners 3D laser et la chaîne de traitement des données brutes nécessaire pour obtenir une représentation 3D précise. Ce travail a permis l’enregistrement détaillé de la stratigraphie dans laquelle le fossile était inclus, avant que celui-ci soit extrait de la cavité. Cette sauvegarde du contexte est très importante si l’on considère les enjeux pour la connaissance de l’évolution humaine que constituent l’étude et la datation de ce squelette unique. Nous concluons en présentant quelques applications, en particulier dans la recherche paléoanthropologique.

In situ 3D scanning of a skeleton of australopithecus at sterkfontein caves (south africa). During more than 10 years of careful excavation, Ron Clarke and his colleagues exposed a virtually complete skeleton of Australopithecus (StW 573, nicknamed “Little Foot”) at Sterkfontein caves, in South Africa. It is now dated of 3.7 million years old [Granger et al., 2015]. This is somewhat older than was published by U-Pb dates for the skeleton [Walker et al., 2006], which, in fact, date a younger flowstone that filled gaps created by subsidence of the breccias containing the skeleton [Bruxelles et al., 2014]. This specimen is exceptional in its completeness and represents a second species of Australopithecus to A. africanus, for which Sterkfontein is well known. Most of the elements of the skeleton are undistorted and preserve anatomical association. However, a few anatomical parts show crushing, fragmentation, scattering, and disarticulation, caused by collapse of portions of the deposit. It has been important to record the details of the skeleton’s position and any displacement within the strata so that the orientation and location of the bony elements are carefully archived prior to removal of the bones from the cave. For this purpose, we scanned the excavation site with two 3D laser scanners. Here we describe the methodology we used to digitize the excavation site including Little Foot. We detail the practical aspects of acquiring 3D views with a laser range scanner and the post-processing computer graphics pipeline required to obtain an accurate 3D representation. We used a Konica-Minolta VIVID 910 scanner which is widely used in industrial metrology and a NextEngine HD scanner which is a low-cost desktop device used to digitize small archaeological objects. Post-processing of the 3D views consists in a pipeline of computer graphics procedures : selection of 3D views, global registration, fusion, and simplification, “beautifying” the resulting 3D reconstruction and rendering. One author used only open-source software whereas another author combined the functionalities of several commercial softwares. We conclude by presenting some applications, in particular in paleoanthropological research. High resolution 3D models provide a memory of the geological context to assist interpretation of the skeleton in relation to the detailed stratigraphy. With the 3D digital models, it will be possible to come back to an interactive and non-interpretative view of the context.