GPS for Dummies.pdf - Engineering Surveyor

58Part II: All About GPSAlthough survey-grade GPS receivers can provide accuracy of less than twocentimeters, they are very specialized and expensive, require a lot of training,and aren’t very portable. Their accuracy is achieved with DGPS and postprocessingcollected data to reduce location errors. The average GPS userdoesn’t need this level of precision.Clouds, rain, snow, and weather don’t reduce the strength of GPS signalsenough to reduce accuracy. The only way that weather can weaken signals iswhen a significant amount of rain or snow accumulates on the GPS receiverantenna or on an overhead tree canopy.Information from GPS ReceiversGPS receivers provide your location and other useful information: Time: A GPS receiver receives time information from atomic clocks, soit’s much more accurate than your wristwatch. Location: GPS provides your location in three dimensions:• Latitude (x coordinate)• Longitude (y coordinate)• ElevationThe vertical (elevation) accuracy of consumer GPS receivers isn’tthat great. It can be within 15 meters, 95 percent of time. Some GPSunits incorporate more accurate barometric altimeters for betterelevation information.Your location can be displayed in a number of coordinate systems, such as• Latitude/longitude• Universal Transverse Mercator (UTM)I cover coordinate systems in Chapter 2. Speed: When you’re moving, a GPS receiver displays your speed. Direction of travel: A GPS receiver can display your direction of travel ifyou’re moving.If you’re stationary, the unit can’t use satellite signals to determinewhich direction you’re facing.Some GPS units have electronic compasses that show the direction thereceiver is pointed whether you’re moving or standing still. Stored locations: You can store locations where you’ve been or want togo with a GPS receiver. These location positions are waypoints. Waypointsare important because a GPS unit can supply you with directions andinformation on how to get to a waypoint. A collection of waypoints that