|
Several recording techniques are used together in Cultural Heritage Documentation projects. The main purpose of the
documentation and conservation works is usually to generate geometric and photorealistic 3D models for both accurate
reconstruction and visualization purposes. The recording approach discussed in this paper is based on the combination of
photogrammetric dense matching and Terrestrial Laser Scanning (TLS) techniques. Both techniques have pros and cons,
and criteria as geometry, texture, accuracy, resolution, recording and processing time are often compared.
TLS techniques (time of flight or phase shift systems) are often used for the recording of large and complex objects or
sites. Point cloud generation from images by dense stereo or multi-image matching can be used as an alternative or a
complementary method to TLS. Compared to TLS, the photogrammetric solution is a low cost one as the acquisition
system is limited to a digital camera and a few accessories only. Indeed, the stereo matching process offers a cheap,
flexible and accurate solution to get 3D point clouds and textured models. The calibration of the camera allows the
processing of distortion free images, accurate orientation of the images, and matching at the subpixel level. The main
advantage of this photogrammetric methodology is to get at the same time a point cloud (the resolution depends on the
size of the pixel on the object), and therefore an accurate meshed object with its texture. After the matching and
processing steps, we can use the resulting data in much the same way as a TLS point cloud, but with really better raster
information for textures. The paper will address the automation of recording and processing steps, the assessment of the
results, and the deliverables (e.g. PDF-3D files). Visualization aspects of the final 3D models are presented. Two case
studies with merged photogrammetric and TLS data are finally presented:
- The Gallo-roman Theatre of Mandeure (France);
- The Medieval Fortress of Châtel-sur-Moselle (France), where a network of underground galleries and vaults has been
recorded.
|
