latitude/longitude information presented on a CDU is too accurate to be utilized for

positioning of the vehicle on a paper map using a pencil.  The accura cy of the

pencil mark (1 mm) on the map is only accurate to 50 m on a l:50000 map. 

Additionally, most of the navigator s problems are not related to the determination

of the vehicle s absolute position, which is what the GPS CDU presents, but its

position relative to obstacles, other vehicles, desired weapon release points, etc.

Only under en route navigation is the navigator interested in his absolute position

when navigating to pre planned waypoints and/or rendezvous positions.  The GPS

derived position data must there fore be transferred to some kind of map to tell the

operator where he is and where he wants to go.  Position information from GPS

displayed on a digital map can be verified by super imposing a radar picture on the

digital map display or by presenting position information from other navigation

systems on the digital map.

13.3.2  Use of Digital Maps for Tactical Displays

Tactical displays are often video screens or other displays which present a

synthetic picture of target position and target course/speed obtained from external

sources or onboard systems (electro optical systems, lasers etc.).  A radar picture

can also be displayed on the same screen to provide a correlation between the

radar picture and the synthetic picture.  There are times when the radar may not be

transmitting, for example, when Emission Control (EMCON) policies are

implemented.  During these times, compensation for HV movement is provided by

an onboard navigation system such as an INS or gyro/log.  Under

such circumstances a digital map display has two limitations:

a. The synthetic picture "drifts" due to INS drift or  inaccuracy in gyro/log

information, if radar updates are not possible.

b. Only limited map information is available on the tactical display.  Paper

maps may have to be used to give a complete picture of the tactical

situation.

These limitations can be eliminated by using digital maps updated by GPS.  The

tactical display picture then has no drift problem because it is constantly updated

by GPS, where all map information including own position, course and speed are

displayed very accurately.  In additional to enhancing the performance of each

individual platform, substantial improvements in multi  platform coordination are

possible due to aligned tactical displays of  the units.

13.3.3  Improvement of Common Reference Grids

The continuous availability of precise GPS position and velocity on participating

platforms can provide numerous enhanced force coordina tion capabilities including:

a. Improved gridlock

b. Geodetic gridlock

c. Sensor calibration

d. Over The Horizon Targeting (OTHT) operations

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