Proceedings of the CIPA WG 6 International Workshop on Scanning for Cultural Heritage Recording

Böhler, Wolfgang

Bibliographic data

Monograph

Persistent identifier:: 830281592

Title:: Proceedings of the CIPA WG 6 International Workshop on Scanning for Cultural Heritage Recording

Sub title:: September, 1 - 2, 2002, Corfu, Greece

Scope:: 159 Seiten

Year of publication:: 2002

Place of publication:: Thessaloniki

Publisher of the original:: Publ. ZITI

Identifier (digital):: 830281592

Illustration:: Illustrationen

Signature of the source:: T 15 B 1303

Language:: English

Additional Notes:: Literaturangaben

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Böhler, Wolfgang

Corporations:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Adapter:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Founder of work:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Other corporate:: International Workshop on Scanning for Cultural Heritage Recording, 2002, Kerkira; ICOMOS/ISPRS Committee for Documentation of Cultural Heritage

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2015

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: 1. INSTRUMENTS AND METHODS

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: MULTISCALE ARCHAEOLOGICAL SURVEY BASED ON THE INTEGRATION OF 3D SCANNING AND PHOTOGRAMMETRY. G. Tucci, J-A. Beraldin, S. Ciofi, V. Damato, D. Ostuni, F. Costantino and S. F. El Hakim

Document type:: Monograph

Structure type:: Chapter

-10- complicated signal analysis, the results may be more accurate (at the expense of the measuring rate). Since a well defined returning signal is needed, scanners using the phase comparison method may also have a reduced range and tend to produce more wrong or dropped points. Laser/Receiver/ Time Measurement Unit rates and real time processing are provided, however, these instruments are an alternative to the scanning devices specified above and may under practical requirements be considered as 3D scanners as well. Object Object 0 Lens Figure 1. Time of flight principle Figure 3. Triangulation principle: double camera solution 3.2 Triangulation scanners Single camera solution. This type of scanner consists of a transmitting device, sending a laser beam at a defined, incrementally changed angle from one end of a mechanical base onto the object, and a CCD camera at the other end of this base which detects the laser spot (or line) on the object. The 3D position of the reflecting surface element can be derived from the resulting triangle (cf. fig. 2). This principle, too, has pre decessors in surveying where range finders with constant bases have been used. From there, it is also well known that the accuracy of the distance between instrument and object decreases with the square of this distance. Obviously, for practical reasons, the base length cannot be increased at will. Nevertheless, these instruments play an important role for short distances and small objects where they are much more accurate than ranging scanners (cf. fig. 4). Figure 2. Triangulation principle: single camera solution Double camera solution. A variation of the triangulation principle is the use of two CCD cameras, each one at another end of the base. The spot or pattern which is to be detected is generated by a separate light projector which does not have any measuring function (cf. fig. 3). A large variety of solutions can be found. The projection may consist of a moving light spot or line, of moving stripe patterns, or of a static arbitrary pattern. The geometric solution is the same as with the one camera principle, thus resulting in the same accuracy characteristics. Not all devices using two cameras offer high point rates and not all of them produce 3D coordinates in real time. If high point 4. ACCURACY CONSIDERATIONS Accuracy is not always the predominant demand in cultural heritage documentation. A standard deviation of a few millimeters for a single scanned surface point is not of much evidence if this point is part of an element possessing a regular geometry (plane, cylinder or the like) and is just used to find the parameters describing this element in a CAD representation. If irregular surfaces have to be modeled (usually by a mesh representation), noisy point clouds can be a rather nuisance in processing, especially when the presence of edges does not allow overall smoothing operations. Therefore, the scanning procedure should be carried out with the most accurate scanner available for the size and range of the particular object. Since objects of many different sizes occur in cultural heritage documentation, no single scanner can really be recommended for all tasks. Instead, a selection of three different scanners co vering roughly the ranges 0.1 to 1 m, 1 to 10 m, and 10 to 100 m is desirable. A large selection of scanners for ranges below 1 m is available (tab.l); a single point accuracy of 0.1 mm and below can be expected. For the mid range from about 1 to 10 m, the MENSI S10 and S25 (former names: SOISIC SD and LD) triangulation scanners are presently the optimal choice (0.5 mm at 2 m, 2 mm at 10 m, for the S25). For larger distances, again a good choice of instruments can be found (table 1), yielding an accuracy of a few millimeters to some centimeters depending to some extent on their possible maximum range. D istance Figure 4. Scanner accuracy (Small parabola: triangulation scanner with short base. Large parabola: triangulation scanner with long base. Straight line: Ranging scanner)

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