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Emerald Group Publishing Limited
Copyright © 2010, Emerald Group Publishing Limited
Metrology and 3D measurement
Article Type: Viewpoint From: Sensor Review, Volume 30, Issue 2
Keywords: Optical measurement, Measurement, Image sensors
Having worked in this field for the past 22 years it is possible to reflect on the developments and to consider the future. During my PhD at City University, London, I developed one of the early optical triangulation sensor systems for measurement of structures as small as water pipes and as large as railway tunnels. I realised that this system was capable of producing cross sections of tunnels, but if I applied the system in a different way, I could produce 3D models of objects. By way of illustrating the capability of this system I measured a manikin, a boat, a polyhedral object, a corridor and the complex shape of a model of a roof. While this was interesting in the late 1980s there were problems. No one had any need of the information and further visualising the data was more than most computers were capable of! Just to remove hidden lines took hours, surface rendering was not a realistic possibility except in programs I wrote myself using graphical tricks to cut down the processing time.
Scroll on a few years and the Laser Tracker was making it debut. This tool provided in a single step a huge leap in accuracy and portability of measurement together with a price tag to match. This tool enabled metrology to move beyond collimators and theodolites and metrologists have not looked back since. Cheaper and simpler metrology tools in the form of articulated arms provided the same ability to measure objects accurately and with a higher level of portability. It was not long before this six-degrees-of-freedom tool was being integrated into a light striper which effectively allowed the three dimensional shape of any object to be captured, reverse engineered and checked. Computing power and graphics were gradually coming together to provide a hugely useful functionality. The Laser Tracker did not stop developing and new developments have resulted in the same six degrees of freedom functionality which allows Laser trackers to operate much more like coordinate measurement machines and also like articulated arms with light stripers attached. It was a particular pleasure to take a part in the development of this technology with Leica.
So, where are we now and where are we going? Well we are not waiting for visualisation’s any longer. We are now wondering how we are going to make use of the huge quantities of information at our disposal. Sensors that measure distance using optical triangulation have been joined by others using different technologies. Whereas, 20 years ago I had to make my own, now we can all buy them off the shelf at reasonable prices. Sensors are now used to provide feedback to many operations such as manufacturing, parking aeroplanes, docking space vehicles and even parking your car. Over the past few years many of us that were once involved in research and development are now involved in commercial exploitation of these technologies. Both challenging things to do. I, for one, have loved every minute of both experiences.
The future holds many challenges and surprises. It is difficult to make a stab as to the future shape or use of the technologies but not the means by which it is likely to be created. In the past one person, or a few persons, have been able to make a significant contribution. The moves over the past few years have been towards technology creation based upon the efforts of teams or multiple teams of people. Consider, Duane Brown, who was the father of a large percentage of the methods used in photogrammetry, which have remained largely unchanged today. He was able to develop a company based around his technology and have nearly a ten year lead over his competitors. Recently, any serious step change in technology will require a team and that team will use tools and technologies already developed by other teams. Take for instance, Google Maps with it is street view feature which allows the operator to navigate through a collection of images which provide a virtually seamless view of a street or a building. Such software technologies are built upon the foundations of GPS, high resolution cameras, software visualisation engines and, no doubt, a team of developers as well as teams of surveying vehicles that will gradually map all the major towns in the country. Ultimately these new developments will be of use to those mapping as-built processing plants to facilitate tasks such as measuring distances to flanges to replacing or repairing existing components. A further point is that many of the technologies that 15 years ago we were experimenting with have arrived in the market place not in the expected industrial applications but in entertainment and for uses not conceived at that time. Examples would be the Wii and the iPhone. I am looking forward to what the future will bring, for myself it never arrives quickly enough.
Tim ClarkeOMS Limited, Bishops Stortford, UKtim@optical-metrology-services.com