GPS for Dummies.pdf - Engineering Surveyor

98Part II: All About GPSTry moving your GPS receiver to watch the satellite signal strength change. Ifsignals are weak or you get a message about poor satellite coverage, move toanother location and change the position of the receiver to better align it withthe satellites that are shown onscreen. If you’re successful, you’ll see newsatellites acquired, the signal strength increase, or both. The more satellitesyou acquire and the stronger the signals, the more accurate your receiver is.Holding the GPS receiver properly will optimize signal reception. If your GPSreceiver has a patch antenna, hold it face up, parallel to the ground. If yourGPS receiver has a quad helix antenna, hold it straight up so that the top ofthe receiver is pointing toward the sky. Chapter 3 covers the differencesbetween patch and quad helix antennas.After the GPS receiver gets enough information from the satellites to fix yourlocation, the screen typically displays an Estimated Position Error (EPE)number. Based on the satellite data received, this is the estimated error forthe current position. The smaller the number displayed, which will be in feetor meters, the more accurate your position.Estimated Position Error (EPE) is a bit confusing. If you see an EPE of 20 feet, itdoesn’t mean that you’re within 20 feet of the actual coordinates. You’re actuallywithin up to two times the distance of the EPE (or even more) from theactual location. For example, if you have an EPE of 50, your location could be1–100 feet of the actual coordinates. EPE is not a maximum distance away fromthe actual location; it’s only a measurement estimate based on available satellitedata. To complicate things even further, different GPS receiver manufacturersuse different formulas for determining EPE, so if you set three different GPSreceiver brands next to each other, they all display different EPE numbers.Some manufacturers are conservative with their numbers, and others are optimistic.Don’t get too caught up with EPE numbers; just treat them as ballparkestimates — and remember, the smaller the number, the better.Changing Receiver SettingsAfter you initialize your GPS receiver for the first time, you need to change afew of the receiver’s default system settings. You only need to do this once,and a few GPS receivers will prompt you to make some of these changes aspart of the initialization process. These changes are mostly to customize settingsbased on your location and needs. Check your user manual for specificinformation on how to change the system settings described below. An exampleof a GPS receiver system settings page is shown in Figure 5-2.