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Images and Artefacts of the Ancient World$
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Alan K. Bowman and Michael Brady

Print publication date: 2005

Print ISBN-13: 9780197262962

Published to British Academy Scholarship Online: January 2012

DOI: 10.5871/bacad/9780197262962.001.0001

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Three-Dimensional Laser Imaging in an Archaeological Context

Three-Dimensional Laser Imaging in an Archaeological Context

Chapter:
(p.88) (p.89) Chapter 9 Three-Dimensional Laser Imaging in an Archaeological Context
Source:
Images and Artefacts of the Ancient World
Author(s):

Andrew M. Wallace

Publisher:
British Academy
DOI:10.5871/bacad/9780197262962.003.0010

This chapter discusses the strengths and weaknesses of techniques of 3D laser imaging based on time of flight and triangulation. Laser scanning by triangulation is a fully developed technology. Through this method, it is now possible to create faithful 3D datasets from a reasonable range of surface materials. However, laser scanning has some certain drawbacks, restricting their universal applicability. For surfaces with concavities or with intricate details, occlusion may occur due to the necessary separation of the viewpoint between the viewing camera and the laser projector. In addition, the data may be corrupted by false and poor returns caused by variable material reflectance. In the time of flight system, the distance is measured by measuring the time for a focused laser beam to impact on and return from the surface of interest. In this method, the distance is computed and a 3D image can be created if the laser beam is scanned across the target. Although, the time of flight method is a more attractive alternative as it eliminates occlusion, it has disadvantages as well. The time resolution necessary to measure the range to sub-millimetre accuracy is difficult to achieve and the measured time is also affected by the magnitude of the returned signal. In addition to reviewing the pros and cons of this current technology, the chapter also discusses the development of a new approach to time-of-flight laser imaging based on time-correlated single photon counting. This new method has various advantages compared to the old methods. It has the ability to make 3D measurements on distance, poorly reflecting or transparent surfaces.

Keywords:   3D laser imaging, time of flight, triangulation, laser scanning, laser scanning by triangulation, occlusion, material reflectance, time of flight system, laser beam, 3D image

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