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.

4.6.2 Platform class
The Jupiter GPS receiver supports three platform 

classes: 

pedestrian (low dynamics
automotive (medium dynamics)
aircraft (high dynamics)

The platform class is set by the OEM to optimise 

navigation processing for the dynamics of the 

specific platform that is carrying the receiver. The 

class is used to set process noise parameters, 

velocity decay time constants, and speed and 

altitude limits. 

The default platform class is automotive. The 

OEM sets the platform class using the Application 

Platform Control message (binary Message 1220). 

The platform class is stored in EEPROM, so it is 

retained when power is turned off. 

This platform class is used when the receiver is 

mobile in a low dynamic environment. An example 

would be a hand-held GPS receiver used for 

hiking.

This platform class is for moderate dynamic 

environments where altitude is not constant. 

A common example would be a car, truck, or 

motorcycle. 

This platform class is for high dynamic 

environments where altitude may change rapidly. 

4.6.3 Navigation cycle
The navigation software nominally executes once 

per second. During each execution, the navigation 

state is propagated forward to the current time and 

updated with any available measurements. The 

navigation solution is then provided to the serial 

interface for output in the selected message set 

(either Navman binary or NMEA).
Note: NMEA may be slightly delayed compared to 

User state propagation over the measurement 

update interval, nominally one second, is by dead 

reckoning with constant tangent plane velocity. The 

tangent plane is defined by the current position 

and the selected datum. This means that if the 

vertical velocity is zero, the state propagation will 

be at constant altitude in the user-selected datum. 

For Pedestrian, Automotive, and Aircraft platforms, 

user state propagation is in three dimensions. 

Once the receiver has been navigating and a 

velocity has been established by the Kalman filter, 

it will be used to propagate the state forward in the 

absence of further measurements for a limited time 

period, until the estimated errors in the propagated 

velocity have reached certain limits. Once these 

limits are reached, Pedestrian (low dynamics). 

Automotive (medium dynamics). Aircraft (high 

dynamics), the velocity estimate is considered less 

reliable and is decayed exponentially with platform 

class dependent time constants.

Once four satellites are available above the 

elevation mask angle with ephemeris data and 

sufficiently good geometry, the Kalman filter begins 

to process the measurements. The Kalman filter 

processes two measurements for each satellite, 

the integrated carrier phase measurement (also 

known as carrier-smoothed pseudo-range) and the 

Doppler, or range rate, measurement.

The receiver uses altitude aiding if a source is 

available and the Expected Vertical Position 

Error (EVPE) exceeds a threshold. The sources 

available for aiding, in the order of preference for 

use, are: 

1 user-entered altitude. 
2 held altitude. ROM altitude (acquisition only).
3 ROM altitude (acquisition only)

The ‘user-entered altitude input’ message (binary 

Message 1219) is used to supply an altitude to 

the receiver. The altitude can be specified as 

instantaneous, valid until cleared from RAM, or 

valid until cleared from EEPROM. Instantaneous 

altitude is valid for one navigation cycle only. 

This altitude input type is used when there is a 

continuous source of external altitude data. 

Held altitude is stored in the receiver when the 

navigation solution is valid. The held altitude is 

stored with a variance that grows from the last 

time it was updated to reflect the age and growing 

uncertainty of the altitude estimate. 

Use of held altitude is normally a significant 

performance boost in an urban environment with 

heavy blockage and it is enabled by default. A 

held altitude value is discarded if the estimated 

climb rate magnitude exceeds 1 m/s. The OEM 

can disable the use of held altitude using the ‘nav 

configuration’ message (binary Message 1221).

When the receiver is not using DGPS, satellite 

measurements include time varying range errors.