guidelines set by the GGF.
Several toolkits have been developed that use the Grid as a mechanism for bring- ing HPV resources to the user’s desktop. In the context of visualization, this chapter showed that there are four categories of Grid Based Visualization user: e-Scientists, Application Scientists, Grid and Visualization Specialists and Visualization Special- ists. Each of the toolkits has been developed and targeted at either e-Scientists or Visualization Specialists, who have some specialist knowledge. e-Viz, a project which was developed in parallel with this research, was developed to target Ap- plication Scientists, using an autonomous approach to helping make decisions for inexperienced user’s.
3.6
Grid enabled AR?
This review identifies several approaches to AR, although the most successful of these rely upon markers to align the virtual artifacts with the real world. More so- phisticated approaches are possible but they are not widely used due to the inherent computational overhead typically involved. There has also been very little research done into using HPV resources to render the virtual objects within the AR scene and to use the pose estimation to steer the virtual camera in the remote simulation. Chapter 5 presents our unique approach to AR, by extracting feature points from the user’s view to allow us to estimate the movement of any arbitrary object in the real world. Chapter 6, shows how the e-Viz framework can be used to remotely render large data-sets which form the virtual objects in our AR scene. To ensure real-time performance this thesis also shows how the pose estimation component of our AR system can be distributed to a remote computational resource.
Chapter 4
Optical Tracking for AR
4.1
Introduction
In order to investigate the research hypothesis a challenging AR application was se- lected. Transcranial Magnetic Stimulation (TMS), is a procedure in which electrical activity in the brain is influenced by a pulsed magnetic field [149]. TMS is extremely important for researchers as it allows them to accurately stimulate different regions of the brain’s cortex and by recording the subject’s response it is possible to validate the function of different areas of the brain. TMS has also been found to be useful in therapy and has had positive results when attempting to treat severe depression, auditory hallucinations and tinnitus as well as other drug resistant mental illnesses such as epilepsy.
Common practice during the TMS procedure is to place an electromagnetic coil on the subject’s head so that it is aligned with a region of interest on the cortex of their brain. The coil and subject’s head can be tracked using optical sensors, and targeting information is calculated and displayed on a local workstation. This procedure allows analysis of the visually induced perceptions related to the cortical
4.1. Introduction 91
site stimulated.
Typical TMS installations utilize a Polaris optical tracking system, as developed and manufactured by Northern Digital Incorporated (NDI), to track the patients head and to help align the electromagnetic coil with the regions of interest on the surface of the patient’s cranium.
This chapter describes the software prototype developed for interfacing with the Polaris optical tracking system that allows users to find the quaternion and trans- lation position of each of the tools. A custom OpenGL application is then used to allow the operator to identify and specify regions of interest in the cranium. The software also guides the operator to accurately align the coil with the specific regions and then uses VTK to render the patient’s brain according to the operator’s view- point, allowing for both an offset calibration for the tools and real-time movement of the patient and operator.
(a) (b)
Figure 4.1: A typical electromagnetic coil (a) and the magnetic field generated (b) as used for TMS.
4.1. Introduction 92
TMS has an important role in neuroscience as it allows researchers to understand which regions of the brain are actually used to perform different tasks. Previously it has been possible to use noninvasive techniques such as fMRI to allow researchers to identify which regions of the brain are active whilst the subject is asked to perform specific tasks. However TMS has now been proved to show that although an area of the brain is active with a task it does not necessarily show that it controls the task.
4.1.1
Clinical uses for TMS
TMS has been shown to have successful results when used for both diagnostic and therapeutic uses:
Diagnostic Uses
TMS allows clinicians to meanure the activity and function of specific parts of the human brain. To date the most widely accepted use is for measuring the strength of a connection between the primary motor cortex and different muscles within the body. This makes TMS a useful diagnostic and assessment tool for cases involving strokes, spinal cord injury, multiple sclerosis and motor neuron disease [150].
Therapeutic Uses
Herrmann and Ebmeier used TMS to show that by exciting specific neurons in the cortex of their trial subjects, they were able to treat them for depression [151]. Based upon this previous work the American Psychiatric Association launched the NeuroStar TMS TherapyTM system in 2006, a clinical trial designed to evaluate TMS as a real world treatment for several depressive disorders.