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A Prototype Optical Tracking System Investigation and Development - page 16 / 170





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Introduction and Background

Figure 1.1 The FastSCAN Cobra(TM)is shown in this figure. It is capable of scanning the surfaces of objects and building intricate 3D models using a PC.

nother difficulty with the Fastrak system is the limited volume in which it operates. Us-

ing the standard transmitter, this is a sphere with a radius of approximately 76 cm, and tracking outside of this volume leads to lower quality tracking data [9]. Scanning of larger objects requires multiple scans to be ‘spliced’ together which is time consuming. These difficulties have motivated SL to investigate different tracking technologies in the hope of increasing the tracking range and enabling their scanner to work with ferromagnetic


It is believed that an optical tracking system could be used to augment the current system and lead to a hybrid design that may overcome the problems associated with magnetic tracking. Optical systems do not rely on magnetic properties to operate and therefore fer- romagnetic objects do not affect these systems. The placement of the optical ‘markers’ (light sources) used in these systems dictate the extents of the ‘tracking volume’. This is

the 3D space that tracking occurs in. By adding more markers, tracking volumes may be extended relatively easily. However, using light sources introduces new problems such as reflections from shiny surfaces and interference from ambient light. Occlusion of optical

markers can also be a problem. both types of design.

hybrid system could overcome the problems inherent in

The purpose of this work is to design and build a prototype six Degrees-of-Freedom (DOF) optical tracking system that can be used with FastSC N. This system will enable the scan- ner’s pose to be determined as it moves in 3D space. The Cartesian X, Y, and Z coordinates and the yaw, pitch, and roll comprise the six DOF.

rigid array of cameras operating in the visible light spectrum detect fixed light sources around the periphery of a room. These cameras are attached to the laser scanner. By continuously calculating the cameras’ positions relative to these fixed light sources, the

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