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The aspects of choosing and creating an optimal workflow to realize a complete digital documentation on an archaeological excavation are manifold. This includes external requirements as costs, comfortable equipment transportation, handling of hardware, sensitivity to weather and climate conditions, as well as questions regarding the time effort, spatial coverage of the archaeological records and accuracy. Finally the precision of the results and the possibilities concerning post-processing of legacy data has to be taken in account. In order to meet the requirements of a complete digital 3D documentation there are nowadays two options for archaeological excavations. One is based on large and expensive equipment – the optical measuring technique by using a 3D laser scanner combined with proprietary control software, the other uses a photogrammetric method ("structure from motion") based on low-cost, small equipment (digital camera) and Free and Open Source Software (Bundler/PMVS/GRASS GIS). Both methods were recently compared at the same archaeological excavation site "Ostia Antica" under the same conditions. Both methods were able to attain the desired results – a 3D point cloud. However, not only the acquisition equipment (hardware) differed but also the post-processing software. On one hand, a proprietary system was used, on the other a FOSS package. To obtain a final result which can easily compared concerning the parameters mentioned above – a 3D point cloud in a geo-referenced environment was needed. For this, the FOSS GRASS GIS (http://grass.osgeo.org/) was further developed by applying an appropriate 3D transformation algorithm. In our talk we will present a list of pros and cons, the potential of both approaches, so that everyone can decide which methodology (or combination of digital techniques) will be appropriate for their certain needs of each excavations.

structure from motion, image-based modeling approach, 3D geo-spatial field technology, archaeological data acquisition, 3D laser scan, FOSS, GRASS GIS, high resolution digital documentation technique