Navman 11 User Manual

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MN002000A © 2004 Navman NZ Ltd. All rights reserved. Proprietary information and specifications subject to change without notice.

The navigation software initialises and maintains a 

state vector which is used to report time, position, 

and velocity to the user. The navigation software 

uses pseudo-range, integrated carrier phase, and 

Doppler measurements from the satellites, and 

external altitude inputs if available. An eight-state 

Kalman filter estimates position, velocity, and clock 

errors.

The OEM has substantial control over the 

operation of the navigation system to customise it 

for a specific application.

4.6.1 Geodetic datums
Geodetic parameters are used in both input and 

output messages. The receiver reports position as 

a set of geodetic parameters (latitude, longitude 

and altitude) in the geodetic position status output 

message (binary Message 1000). Geodetic 

parameters are also reported in the GPS fix 

data message (NMEA Message GGA), with the 

substitution of Mean Sea Level (MSL) altitude 

for geodetic altitude, and in the recommended 

minimum specific GPS data message (NMEA 

Message RMC) as latitude longitude. The receiver 

expects geodetic parameters as part of the 

geodetic position and velocity initialisation input 

message (binary Message 1200). 

Whether geodetic parameters are used as input 

or output data, they are always referenced to the 

currently selected geodetic datum. Each geodetic 

datum is defined by five parameters:

The semi-major axis. 
Flattening of the reference ellipsoid. 
Delta X component of the WGS-84 datum 

origin offset. 
Delta Y component of the WGS-84 datum 

origin offset. 
Delta Z component of the WGS-84 datum 

origin offset. 

The receiver has 189 pre-defined user datums 

selectable by the OEM. These datums, together 

with their identification codes, are listed in 

Appendix E of this document. All of the pre-defined 

datums are taken from the US Government 

document, Department of Defense World Geodetic 

System 1984.

The default datum is WGS-84 (defined as datum 

code zero for the receiver). Other datums are 

selected using the Map Datum Select message 

(binary Message 1211). The selected code 

is reported back in the position status output 

message 1000 or 1001. 

For example, if the receiver was in Navman binary 

mode and the OEM wanted to use a previously 

recorded position to initialise the receiver, and then 

get reported positions in WGS-84, the OEM would 

send three messages to the receiver as follows:

1 Send a ‘map datum select’ message (binary 

message (1211) with the desired datum code 

(the new datum code is reported back in 

message 1000 and/or 1001 if either or both 

messages have been enabled). 
2 Send a ‘geodetic position and velocity 

initialisation’ message (binary Message 1200) 

with the correct latitude, longitude, and altitude. 
3 Finally, send another message 1211 with the 

datum code 0 to set the datum back to WGS-

84. 

The selected datum is always stored in EEPROM, 

so that it is saved during power-off and reset 

cycles. The Navman binary Map Datum Select 

message must be used to change the geodetic 

datum; the datum cannot be changed when in 

NMEA mode. NMEA outputs will use the last 

datum selected in binary mode or WGS-84 if a 

datum selection has never been made.

Besides the 189 pre-defined datums, the OEM 

can define five custom datums for a specific 

application. Each datum is defined by the five 

parameters described in section 4.6.1 and the new 

datum definition is sent to the receiver using the 

User-Defined Datum Definition message (binary 

Message 1210). 

There are five custom datum codes to choose 

from, 300 to 304. All user-defined datums are 

stored in EEPROM. Once the datum is stored, it 

is selected using the Navman binary Map Datum 

Select message in the same manner as the 

pre-defined datums. If a custom datum is stored 

and later re-defined, the existing datum will be 

overwritten.