Richard THOMA
(ARDIG – Archäologischer Dienst GesmbH, St. Pölten, Austria)

Keywords: SFM 3D photos documentation visualisation

Structure from motion (SfM) is a photogrammetric range imaging technique for computing three-dimensional structures from two-dimensional image sequences that may be coupled with local motion signals. To find correspondence between images, features such as corner points (e. g. edges with gradients in multiple directions) are tracked from one image to the next. Correspondences tracking is based on multiple – mostly matrix-addicted – algorithms.
The method provides accurate and comprehensive 3D-documentation of any object when a sufficient sample of photos has been taken at different angles and – likely – similar light setting. Scale does not matter, from a small artefact to large excavation areas SFM can provide (supplementary) documentation data. Due to the highly detailed 3D-content many forms of visualisation are offered.
Result of the computed data is an excellent 3D-Point-Cloud which can be evaluated both by exact (and georeferenced) measurement and archaeological interpretation.
In addition to the implementation in CAD-software, the export for GIS, 3D-visualisation-software or 3D printing stations is also possible. 3D-PDF ensures rendering and working with the data without additional, proprietary software.
Necessary equipment such as camera and total station are already available at most archaeological excavations.
Low additional costs on site – adding most detailed information of the object.
If enough images are available, even destroyed objects from the past can be documented in hindsight. According to sufficient photographic heritage even “historic” excavations can be computed.
As shown in the poster as case study the documentation of „Terrasse 7“ of „Schloß Hof“, a part of the baroque garden area, an complete 30 meter long baroque wall could be calculated from a sample of 120 photos. With the 3D-model the structure of the wall building can be investigated, measured and interpreted.