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GPS
(Global Positioning
System) devices are now freely available and at a low cost. Since the ending of Selective Availability the accuracy of these devices has increased by leaps and bounds. They are now quite capable of being used to collect track or way point data that can be used as the basis of a map. If correction data is available to you then the level of accuracy that can be achieved is very impressive.
The four main GPS manufacturers – Trimble,
Garmin, SiRF and Magellan sold around two million units in the year
2000 alone. An impressive volume but there is more to come. In the United States the Federal Communications Commission have set a requirement
that cell phones must be capable of providing location information. This means that a GPS capability must be added to the millions of cell phones that will be sold in the USA. As a minimum, this enormous additional sales volume will drive down component prices to even lower levels that we see today. We might also see cell phones capable of displaying GPS output to the user available around the world and we might also see combined phone/PDA devices with an interactive mapping capability built into a single unit.
Converting the output of your GPS system into a map is much the same as the process of taking a set of grid co-ordinates collected any other way and loading these into your mapping software. Depending upon the software you use it may be necessary to convert between co-ordinate systems to achieve this. Our own AditMap will happily load GPS track and waypoint information to create an instant map ready to be edited (if necessary) and saved onto your PC. If you are a user of our AditSite recording software then you can output selected items that you wish to visit to your GPS and then use your device to navigate to the exact locations.
AditTrec
Don't tell anyone, but you can now get hold of a program that runs on Palm OS® handheld computers, that can be fully integrated with AditSite. More information on AditTrec
In the UK you can use freely available Internet resources to correct GPS readings, convert data to the UK Ordnance Survey grid references and to adjust heights to those above mean sea level (the Newlyn datum). These services are available at http://www.gps.gov.uk/
If you are living or working elsewhere in the world then you will have to track down any locally available services or use one of the many available data conversion tools.
A low cost solution might be to use two GPS devices.
If one is located at a known point not too far from
the device being used to carry out the survey then
variations in the indicated location of the GPS at
the fixed point could be used to correct the data
being collected by the survey GPS.
For more information on GPS and GPS devices try http://www.gpsworld.com
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