Soils 620

Global Positioning System

Global Positioning Systems (GPS) was developed by the military to determine a location on earth using triangulation from satellites (satellite geometry). There are 24 active government owned satellites circling the earth and a GPS ground instrument must be able to send and receive the single from three satellites for triangulation. The satellites must be visible by the GPS unit so trees and buildings can prevent the GPS unit from working. The military put a random single on top of the correct single from the satellites so that calculation using a GPS unit are not correct unless corrected using a base station with a known location. A detailed explanation of how GPS work is presented by Trimble a company that makes GPS units.

Using a hand held GPS unit measurer the location of the surveyed point in the horseshoe at New Mexico State University. This is called Rilley Point and is north latitude 32 degrees 16 minutes and 55.93452 seconds , west longitude. 106 degrees 45 minutes 15.16430 seconds at an elevation of 3825 feet.
The location with the hand held GPS unit can be as much as 300 feet deferent from the correct location. Determine the distance and direction error of the GPS unit by putting the latitude and longitude. locations give for the site and determined by the GPS unit into a computer program that will calculate the difference between two locations.

Check setup of GPS unit to make sure it is set for the correct Geodesy

Last modified 11/15/97