-------------------------Monitor------------------------ The Newsletter for PC-Based Data Acquisition and Control Issue 89 www.windmill.co.uk December 2005 --------------------ISSN 1472-0221---------------------- A very happy new year to you. This year's final issue contains an example of how Windmill is being used in a project to locate moving vehicles, and an article on the differential global positioning system. The Excel Corner, however, is having a Christmas holiday. We hope you find Monitor useful, but should you wish to cancel your subscription you can do so at http://www.windmill.co.uk/newsletter.html CONTENTS ======== * Windmill News: Locating Moving Vehicles * What is a Differential Global Positioning System? * What next for Satellite Navigation? ________________________________________________________ ________________________________________________________ Windmill News: Locating Moving Vehicles ________________________________________________________ David Wilkinson Associates Ltd, experts on the safe and efficient movement of trains, have recently been working on a DGPS project to locate moving vehicles. (DGPS stands for Differential Global Positioning System.) Whilst developing this system they used the free Windmill software to extract data from a Garmin GPS18 receiver to a laptop computer. They found it easy to set up Windmill to extract the data they needed, using the LabIML Help facility. Once the required settings were entered, the data appeared in the Windmill DDE programme. They then exported that data to Excel using DDE (dynamic data exchange). David Wilkinson is happy with the Windmill software, but he has experienced some difficulties with Windows and the GPS drivers. "The Windmill software works without any problem. The main problem I have experienced so far is due to the fact that when you plug the GPS18 receiver into a laptop, Windows sometimes detects the RS232 data as indicating that a serial mouse has been plugged in. This causes the screen to behave erratically and you have to wait till the Windows system has settled down before trying again." The settings the company used with Windmill were: * Reading Protocol: Continuous Flow * Instrument Idle or Wait Time: 0 * Returned Message Length: 60 * Instrument Initialisation String: none * Baud rate: 4800 * Flow control: None David Wilkinson Associates Ltd was formed in 1997 as an independent railway engineering and safety consultancy. They can be reached at http://www.e-railways.co.uk/ For a later version of the software see http://www.windmill.co.uk/https://www.windmillsoft.com/daqshop/rs232-modbus.html Further Reading =============== Interfacing a Garmin GPS http://www.windmill.co.uk/garmin.html ________________________________________________________ ________________________________________________________ What is a Differential Global Positioning System? ________________________________________________________ A differential global positioning system, or DGPS for short, provides very accurate location information. It does this by correcting errors in the GPS errors. The original GPS was developed by the US Department of Defense. Briefly, GPS satellites broadcast radio signals containing their position and time. A GPS receiver picks up signals from at least four satellites. The receiver knows exactly where in the sky the satellites are, it just doesn't know exactly where on earth it is. Until, that is, it determines its distance from the satellites. It does this by calculating the time it took for the signals to reach it. However, signals may be delayed as they bounce off obstructions like mountains, buildings and particles in the atmosphere. Differential GPS compensates for these timing errors. With DGPS a reference is fixed in a known position. Instead of using timing to calculate position, it uses its position to calculate timing. It works out the difference between the actual time a GPS signal takes on its journey and the calculated time it should have taken. It then broadcasts this error correction information to mobile GPS receivers in the area. This error correction technique results, in moving situations, in a 5 m accuracy 95% of the time (source: Northern Lighthouse Board). Much better than the 20 m accuracy of GPS. It also means that a DGPS can check the integrity of each satellite's signal and report whether it is good or bad. Further Reading =============== The GPS: History, Function and PC Interfacing Monitor 30, January 2001 http://www.windmill.co.uk/monitor30.html Connecting a GPS Receiver to a PC http://www.windmill.co.uk/gps.html ________________________________________________________ ________________________________________________________ What Next for Satellite Navigation? ________________________________________________________ The first test satellite of Europe's Galileo navigation system has just been launched. Galileo is a civilian project and promises the permanent provision of a navigation system. The rival US (GPS) and Russia GLONASS) systems are both run by the military and could in theory be turned off at any time. You will be able to take a position with the same GPS receiver from any of the satellites in any combination. The system is designed to deliver real-time positioning accuracy down to one meter. Better than the existing GPS and DGPS systems. The Galileo system will guarantee service under all but the most extreme circumstances and will inform users within seconds of a failure of any satellite. By placing satellites in orbits at a greater inclination to the equatorial plane than GPS, Galileo aims to achieve better coverage at high latitudes. This will make it particularly suitable for operation over northern Europe, an area not well covered by GPS. Galileo is scheduled to be fully operable in 2008 - but you will need a new GPS receiver to make use of it. Further Reading =============== European Space Agency http://www.esa.int/esaNA/galileo.html European Commission http://europa.eu.int/comm/dgs/energy_transport/ ________________________________________________________ ________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see http://www.windmill.co.uk We are happy for you to copy and distribute this newsletter, and use extracts from it on your own web site or publication, providing the above notice is included and a link back to our website is in place. An archive of previous issues is at http://www.windmill.co.uk/newsletter.html and an index of articles at http://www.windmill.co.uk/newsletter.html Windmill Software Ltd, PO Box 58, North District Office, Manchester, M8 8QR, UK Telephone: +44 (0)161 833 2782 Facsimile: +44 (0)161 833 2190 E-mail: [email protected] http://www.windmill.co.uk/ https://www.windmillsoft.com/
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