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CCD based active triangulation for automatic close range monitoring of rock movement

Singh, Rajendra; (1996) CCD based active triangulation for automatic close range monitoring of rock movement. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Automatic close range photogrammetric measurements face a number of difficulties due to depth of field and lack of sufficient texture in high resolution images at close range. These problems increase further for a featureless and low texture object like massive sandstone strata. Using active triangulation as an approach towards this measurement goal, this thesis describes the concept behind and the work carried out for the design of an automated system to measure the surface of massive sandstone strata. After an analysis of the key problems of the projection system, a diffraction grating based diode laser dot matrix was selected to place a large number of high contrast discrete target points on the object. The main idea was to obtain high precision image co-ordinates of the actively placed target points and combine them with known projector orientation for automated high accuracy object space measurement. Accurate centroid location of the target points was done by least squares based template matching which provided a precision of 0.03 pixel for the images of these laser dots. Other practical problems of a CCD based system like data storage and field of view were also considered during the design phase. Different investigations were conducted to visualise the reliability and potential of CCD based vision for coal mining inspection and measurement. A camera model of the laser projector was developed without a control field. Generation of a virtual three dimensional testfield by the observed geometrical characteristics of the projector and application of the bundle adjustment procedure resulted in precise estimation of interior orientation parameters of the laser dot projector. The interior orientation parameters of the projector were found comparable with those of a real CCD camera which were derived using a standard three dimensional testfield. As various distortions of the projector were modelled by treating it as a virtual camera, the intersection accuracy improved during three dimensional object space measurement. This system provided an intersection parallax of 0.3 mm during a laboratory test scan of an object at 4.5 m distance.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: CCD based active triangulation for automatic close range monitoring of rock movement
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Earth sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10104955
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