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:: 5. PROJECTS AND EXPERIENCES

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: EXPERIENCES WITH LASER SCANNING AT i3mainz. Andreas MARBS

Document type:: Monograph

Structure type:: Chapter

• Colonna del Tempio di Hera-Lacinia, Crotone (Italy): Greek Doric column of the last of 48 columns supporting the temple of Hera Lacinia (500-475 BC). Of the whole structure, sacked and damaged by the 1683 earthquake, there remains a single degraded limestone column with its capital halved. The survey results are used for documentation purposes and to compare laser range scanning with traditional photogrammetric techniques. • Nuraghe Iloi, Sardegna (Italy): The nuraghe lloy is a complex archaeological building about five metres tall and consisting of a tower of conical shape, built with layers of enormous boulders without the use of malt cement. The survey results are used for documentation purposes, structural condition studies and visualization. • Hamburg City Centre: This survey was done in the context of city modelling and includes 50 scans covering several streets in the city centre of Hamburg. It shows that laser range scanning allows to quickly acquire detailed 3D information of entire streets and even cities. However, it also shows that for this kind of application the processing software needs to be highly automated and needs to support a sophisticated management of the huge amount of acquired data. Table 1: A list sample objects specifying their type, the acquisition hardware used for the survey and the time required for acquisition and processing. Surveyed object Sagrestia Archivio di Stato Ex Hotel Colombi a Colonna di Hera Lacinia Nuraghe Iloi Hambur g Geometry Inside Inside Outside Outside Outside Laser scanner Cyrax Callidus Cyrax Riegl LPM-HA Riegl Z360 N scans 15 4 11 2 20 Type 2D camera Digital Digital and analog Digital and analog Digital / N images 15 30 12 2 / Time acquisition (hours) 8 12 8 8 8 Time data processing (days) 4 6 4 2 4 The diversity of the presented objects shows the versatility of lasers scanning in the field of architecture and Cultural Heritage. The final 3D models are used for different scopes, confirming the importance of this technology for conservation, maintenance and presentation of Cultural Heritage 3. DATA ACQUISITION The software described in section 4 allows mapping external 2D images on the 3D mesh, which is reconstructed from the raw 3D data. Therefore, data acquisition not only refers to object scanning but also includes the acquisition of the 2D images. It is also possible (although not necessary) to acquire a set of external reference points for geo-referencing. Table 1 lists details of the data acquisition (i.e. type of scanner, time of acquisition) for each of the sample objects. The remainder of this section lists some of the lessons we learned during acquiring and processing the data and could serve as a small guideline for future scanning sessions. 3.1 3D acquisition Usually it requires several scans to cover the entire object and resolve all the occlusions and shadows. The main points to consider are: • Occlusion and shadows: the scanning position should be planned carefully to avoid missing data. Holes and occlusion become particularly evident if the data will be triangulated in a later stage. It is useful if the software gives the possibility to register the acquired scans in situ so that holes and occlusion can immediately be detected and resolved. • Angle of acquisition: the precision of the 3D measurement acquired with the laser scanner decreases with the acquisition angle. A shallow angle also produces a low measurement resolution on the object. To increase the quality of the final model the acquisition direction should be as perpendicular to the object surface as possible. For example, the distance between viewpoints along a façade should not be too long. • Overlap between scans: especially feature-based and point-based registration (see section 4.2.2 and 4.2.3) require sufficient overlap between scans. For example, the ICP registration requires about 30% overlap, which also needs to have some geometrical information in all 3 dimensions (i.e. the overlapping points should not lay on a single plane). If possible, it is useful to acquire one or more reference scans at low resolution, which cover as much of the object as possible and which are then used to register the detailed scans. • Uniform scan resolution: scanner viewpoints and resolution settings should be chosen to yield a fairly uniform resolution on the object in order to obtain a final 3D model with homogeneous geometrical properties. • Documenting the acquisition: Especially if the scan are not registered on the fly, it is important to take note of the data acquisition scheme both for laser scanner viewpoints and the acquisition points of the 2D images, otherwise a lot time might be spent assigning the different scan and images to each other. 3.2 2D images acquisition The 2D data usually is acquired with an uncalibrated standard digital camera. However, it is also possible to use calibrated photogrammetric cameras to increase accuracy or a different wavelength (e.g. infra-red) for special applications. • High quality pictures: the images acquired with the camera are directly mapped onto the 3D model; therefore better images will directly result in a better final result. Special care must be taken to avoid reflections and shadows and to minimise the difference in exposure between images. Even though image balancing is part of data processing (see section 4.5.2), most of the balancing problems should be avoided during the acquisition phase. For inside acquisition the use of artificial light can help to avoid shadows. For outside acquisition, the weather during - 149 -

Access restriction

Copyright

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

Monograph

Chapter

Chapter

Table of contents

Cite and reuse

Monograph

Chapter

Image

Image fragment

Citation links

Citation recommendation