Sebastian VETTER / Gunnar SIEDLER
(Fokus GmbH Leipzig, Germany)

Outline: This work shows automatic generation of digital surface model on the base of images and tacheometrical measured reference points. It shows the creation of true to scale image plans as mapping base on the example of a coloumn. This work also shows the big advantage of controlling the accuracy and quality of the 3D- object documentation with the quality of the images.

Abstract: Digital stereo-photogrammetry / image models allows users an automatic evaluation of the spatial dimension and the surface texture of objects. The integration of image analysis techniques simplifies the automatic image orientation and offers a high accuracy in evaluation. Due to the substantial similarities of stereoscopic image pairs (stereo model), correlation techniques provide measurements of subpixel precision for corresponding image points.

By automatic or manual single point measurement of model- and the 3D-reference points in the images the stereo models are orientated automatically.

An adapted expansion- and matching algorithm offers the possibility to scan the object surface automatically. The result is a three dimensional pointcloud, the scan resolution depends on image quality.

With the help of the implemented triangulation algorithm a digital surface model (DSM) can be created. The texturing can be made automatically by the previously used images. It is possible to texture the surface model in a direct way or to generate orthophotos automatically with support of DSM.

A big advantage is the possibity to control the accuracy and quality of the 3D- object documentation with the resolution of the images. The procedure described here is implemented in software metigo 3D.

In January 2011 different kinds of objects (also floors and facades) were documentated by stereo models with the goal to generate orthophotos at the site of Athribis near the modern village of Nag’ el-Shaykh Hamad in a project of University of Tübingen (Institute for the cultures of the ancient Orient (IANES),  Department of Egyptology).

The coloum described here, was covered with 9 stereo models (image pairs) and 31 reference points, measured by tacheometer. For each stereo model a digital surface model was generated like described above.

In combination with these surface models and a user defined unwind cylinder a true to scale image plan with resoultion 300 dpi and scale 1:10 was created.

Keywords: 3D object documentation, textured surface model, orthophotos, image matching, pointcloud