Applications for GPS

GPS News, Information & Links

Johnny Appleseed G P S - The Theory and Practice of GPS

GPS is one of the most fantastic utilities ever devised by man. GPS will figure in history alongside the development of the sea-going chronometer. This device enabled seafarers to plot their course to an accuracy that greatly encouraged maritime activity, and led to the migration explosion of the nineteenth century. GPS will effect mankind in the same way. There are myriad applications, that will benefit us individually and collectively.

Latitude, Longitude, AMG etc etc etc

I get many requests to explain the different numbers used by different GPS at the same location. This is a valid and sensible question, and there are easily understood answers. You may also wonder about terms such as UTM, GDA, MGA, datum, position format, grid, and true north. My customers get free assistance with these, and any other matter relating to their purchase, and the use of the GPS.

Applications for GPS

- In Australia

Find latitude and longitude of any town in Australia

Articles written by Kimball Thurlow, ©, Johnny Appleseed GPS, Brisbane

Geologist using Garmin eTrex, says this

"I've got a handheld Garmin etrex (the yellow one) which is a great little device and mega easy to use. I'm currently using it to record the positions of unstable rocks in the _____ for our local transport authority. In some locations I can get an accuracy down to 5m which is great. However in other spots, where there is a bit of tree cover or a high rock slope adjacent to the location, the accuracy goes out to 25m or more which is too great. We've considered hiring a _____ unit with the backpack antenna to do these sites; however it costs an arm and a leg to do so.

I'm therefore looking for suggestions. I thought that adding a DGPS facility to the etrex would be the way to go however I don't know if this can be done. Would this be the best way to go to improve on the accuracy? Can you suggest an alternative?"

Well, the answer is that the DGPS is available for the eTrex, as a backpack, to purchase, or for hire. Simply a matter of connecting the eTrex with the supplied cable, and accuracies of 2-3 metres are achievable. However, where some of the satellites are obscured, as in the cases of 25 metre accuracy, it will improve proportionately.

The geologist now has a backpack fitted up by Johnny Appleseed GPS with a Garmin beacon receiver. The location of the job is within 300kms of an AMSA DGPS beacon transmitter. He is very pleased with the result, achieving the accuracies he wants. And the additional cost? - about $1200, and there is no subscription fee.

Footnote: The use of an eTrex Summit or eTrex Vista will also give very accurate elevation readings. So 3 dimensional accuracy may improve to 2-3 metres all round.

Radio enthusiasts pick up other radio operators and stations via radio, and plot them on GPS or computer map

APRS (Automatic Position Reporting System)

A GPS outputs a NMEA String at 4800 baud RS232
A microprocessor receives the string and filters out the $GPRMC NMEA sentence
From the $GPRMC sentence, the Latitude, S/N, Lontitude, E/W is filtered out
A 'packet' is formed and a call sign added
The packet is sent to a VHF radio transmitter, which transmitts tones according to the data fed
A receiving station picks up the tones, decodes them and derives the lat and long
The lat and long are displayed on computer or on the MAP page of a GPS

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System Hardware

GPS --> Mircoprocessor --> VHF Radio --> Antenna
Antenna ----> VHF Radio ----> Decoder ---> Computer with maps

"In the case of the GARMIN GPSMap176 shown on my web page, any stations heard are translated into the NMEA $GP????? Write a waypoint command, back to the GPS." -
from Andrew VK4TEC See the GPSMAP176 with radio locations.