ABSTRACT

Photogrammetry has been In regular use since 1980 to produce three dimensional measurements underwater, for a variety of tasks The paper will briefly summarise the history of The technique, from its inspection orientated origins to the latest engineering related, deep water, ROV surveys, In order to analyse the strengths and weaknesses of the technique This analysis will Introduce the technological Improvements, leading to the satisfactory of market demands, that can be made possible with advancing technology The development of Real Time Photogrammetry, from the feasibility study to offshore trials, will then be introduced, emphasising the enormous possibilities of the technique and its component technologies electronic still Imaging, digital Image data transmission and storage, real time and still stereo viewing, and near Instant three dimensional measurements of complex objects The by-products of the development will also be Introduced, which Include total electronic reporting systems and the database controlled replay of visual data within a networked computer system, with suggestions as to how these could influence structural and pipeline Inspection, as well as engineering surveys In today's, as well as tomorrow's, world

1. INTRODUCTION
1.1 What is Photogrammetry?

Photogrammetry IS a visual imaging technique for the acquisition of accurate three-dimensional measurements without contact with the subject

Photogrammetry IS not a new technique, and has been In use for more than 100 years for the compilation of maps from aerial photography, for topographical surveying and for industrial uses, such as the quality control of large castings

1.2 Why isit used Underwater?

Underwater Photogrammetry provides a fast and cost effective method of obtaining precise three dimensional measurements, for Inspection or engineering purposes It is necessary only to photograph a subject with a pair of photogrammetric cameras, or with a single photogrammetnc camera from two or more camera positions, in such a way as to achieve stereo coverage, to allow accurate measurements to be taken from the photographs

  • It is a non-contact technique, and so there is little or no contact or Interference with the subject

  • It allows measurements of subjects that are difficult to measure by conventional techniques, because of their shape or position

  • It uses separate data acquisition and data processing phases and so it keeps underwater operational time to a minimum

  • Its use is not complicated by a more complex shapes, for example lf many measurements are required to accurately define ihe shape of Impact damage which Included multiple Impacts, tears etc

  • Total effort does not Increase proportionally with the number of points to be measured

  • The analysis process is select we, and so can be tailored to the exact requirement of the application, even though the information density stored on photographic film is enormous

  • The information can be stored archivally on the photographic film, to be extracted, or redefined, at any time

  • The information may be presented In many forms as discrete measurements, sections, contours, plan and elevation drawings, isometrics, contours etc, to best suit the exact requirements of the end user

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