NorthStar 8700 Technical Reference Manual page 24

Section 4 - GPS receivers
PAGE 14
2-D Differential
•
When 3-D differential mode can't be used, this is the
highest-performance navigation mode. The 8700 operates in this
mode when it receives data from only three satellites with adequate
geometry and differential corrections. SC-104 differential corrections
can be taken in on the auxiliary data port using either RS-232 or
RS-422.
3-D Nav
•
When sufficient differential corrections aren't available, this is the
preferred navigation mode. The 8700 operates in this mode when it
receives data from at least four satellites with adequate geometry,
but no differential corrections.
Altitude-Hold (2-D Nav)
•
This is the least-preferred navigation mode. If satellite
measurements are insufficient to produce a 3-D navigation solution,
but sufficient when altitude information is available, the 8700
operates in this mode, where the altitude is assumed constant.
Dead-reckoning mode
The 8700 enters dead-reckoning mode when it can't remain in navigation
mode. The speed and direction of the vehicle are assumed constant to
allow the 8700 to provide an estimated position.
Fault mode
The 8700 enters fault mode from any mode—except initialization—when
and if the 8700 determines that one or more critical system faults are
affecting its outputs. Fault mode supersedes all others, and remains active
until the next power-down/power-up cycle.
05/01/97 REV H