74Section 6GPS ReceiverReferenceIntroduction3D Navigation - at least four satellites with goodgeometry have been locked onto, and your positionis now being calculated in latitude, longitude andaltitude. ‘3D Diff’ will appear when you arereceiving DGPS corrections in 3D mode.Poor GPS Coverage - the receiver isn’t trackingenough satellites for a 2D or 3D fix due to badsatellite geometry.Not Usable - the receiver is unusable, possibly dueto incorrect initialization or abnormal satelliteconditions. Turn the unit off and back on to reset,and re-initialize the receiver if necessary.Simulating Nav - the receiver is in simulator mode.The status bar displays ‘Sim’ on all main pages.‘Need to Select Initialization’ PromptIf no satellites are received for several minutes or aninsufficient number of satellites are received to determinea position fix, a message will appear, prompting you toinitialize the receiver. This allows you to specify a startinglocation from which to search for satellites, or to enablethe AutoLocate feature. It is also useful if you havetraveled over 500 miles with the receiver off. Thismessage will automatically appear when you first use yourNavTalk Pilot. The prompt may also appear duringnormal use if the antenna is shaded or the unit is usedindoors.EPE and DOPThe Satellite Status Page also indicates the accuracy ofthe position fix, using Estimated Position Error (EPE) andDilution of Precision (DOP) figures. DOP measuressatellite geometry quality (i.e., number of satellitesreceived and where they are relative to each other) on ascale from one to ten. The lowest numbers are the bestaccuracy and the highest numbers are the worst. EPEuses DOP and other factors to calculate an estimatedposition error, in feet or meters.Using the Map toInitialize
