Photogrammetric survey of complex geometries with low-cost software: Application to the ‘G1′ temple in Myson, Vietnam

Image-based modelling for cultural heritage documentation is an issue in which photogrammetry plays a fundamental role. Nowadays several commercial software packages (also at low-cost) allow the creation of accurate models by using digital images. However, a solution which automatically creates an accurate digital model from images is not available on the market yet, thus a relevant part of the work is carried out by interactive measurements. In the paper, the full reconstruction pipeline of a temple of the archaeological site of MySon (Vietnam) by using the well-known photogrammetric software PhotoModeler (EOS System Inc., Canada) is illustrated and analysed. In order to speed up the process, an innovative photogrammetric tool that is capable to interact with PhotoModeler's environment is presented. This allows the orientation of the image block in an automatic way without using any target. Then, a point cloud is extracted from the images by using manual measurements of corresponding points to plot vector features or by multi-image matching techniques, in order to automatically provide a reconstruction of the surface of the object. The accuracy of the obtained point cloud is similar to that achievable with range-based sensors. Finally, the point cloud can be interpolated in order to obtain a 3-D surface model. To verify the potential of this method, it was applied to the conservation design of the ‘G1′ temple in MySon, Vietnam. For this real case, which was listed as a UNESCO World Cultural Heritage site, the results of the automatic method for image orientation were compared with those obtainable with manual measurement, and demonstrated a similar accuracy despite a shorter elaboration time. In addition, the application of the photogrammetric 3-D model for planning future restoration activities is reported and discussed.