Garmin Garmis GPS Smart Antenna GP35-LVC - Manual (Page 10)

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1) Latitude/longitude/altitude
2) Velocity
3) Date/time
4) Error estimates
5) Satellite and receiver status
Normally the GPS 35LP will select the optimal navigation mode (2D or 3D) based on available satellites
and geometry considerations. The host system, at its option, may command the GPS 35LP to choose a
specific mode of navigation, such as 2D. The following modes are available:
1) 2D exclusively with altitude supplied by the host system (altitude hold mode)
2) 3D exclusively with altitude computed by the GPS 35LP
3) Automatic mode in which the board set determines the desired mode based on satellite availability
and geometry considerations
When navigating in the 2D mode (either exclusive or automatic), the GPS 35LP utilizes the last
computed altitude or the last altitude supplied by the host system, whichever is newer. The host system
must ensure that the altitude used for 2D navigation is accurate since the resulting position error may be
as large as the altitude error. See Section 4 for more information on altitude control.
The GPS 35LP will default to automatic differential mode – “looking” for real-time differential corrections
in RTCM SC-104 standard format, with message types 1,2,3, or 9, then attempt to apply them to the
satellite data, in order to produce a differential (DGPS) solution. The host system, at its option, may also
command the GPS 35LP to choose differential only mode. When navigating in the differential only
mode, the GPS 35LP will output a position only when a differential solution is available.
2.4 SATELLITE DATA COLLECTION
The GPS 35LP will automatically update satellite orbital data as it operates. The intelligence of the GPS
35LP combined with its hardware capability allows these data to be collected and stored without
intervention from the host system. A few key points should be considered regarding this process:
1) If the receiver is not operated for a period of six (6) months or more, the unit will “search the sky”
in order to collect satellite orbital information. This process is fully automatic and, under normal
circumstances, will take 3-4 minutes to achieve a navigation solution. However, the host system
should allow the board set to remain on for at least 12.5 minutes after the first satellite is acquired
(see Section 4 for more information on status indications).
2) If the memory backup battery fails, the receiver will search the sky as described above. Should
the memory battery discharge, the unit needs to be powered on for several days to insure a
sufficient recharge to maintain several months of clock operation and memory storage. System
configuration information will not be lost due to battery discharge, only previous position, time and
almanac data will be lost.
3) If the initial data is significantly inaccurate, the receiver perform an operation known as
AutoLocate™. This procedure is fully automatic and, under normal circumstances, will require 1.5