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the GPS 35/36 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 35/
36
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 35/36 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 35/36 will default to automatic differential
corrections, attempting 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 35/36 to
choose differential only mode. When navigating in the
differential only mode, the GPS 35/36 will output a position
only when a differential solution is available.
2.4 SATELLITE DATA COLLECTION
The GPS 35/36 will automatically update satellite orbital
data as it operates. The intelligence of the GPS 35/36
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 GPS 35/36 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
