Table of Contents
Advertisement
8.2 Noise estimation and Weights
Position estimation is calculated as weightened sum of all filtered selected ref-systems measurements. Weights are
automatically calculated as function of noise estimated (lower weight corresponds to ref-system with higher noise).
Weight can be corrected in details window – see Section 8.8.4, page 150.
Estimated noise for each ref-system is the result of Kalman-based filtering. RMS value of estimated noise value is
shown in Ref window.
8.3 Biasing
Bias of each Ref-system includes the following components:
1. Initial offset;
2. Jump estimation;
3. Slow drift estimation.
The position-reference system which starts as the first reference has a zero offset.
The second position-reference system will have some offset to provide continuous position estimation.
Jump is estimated by the filter when Ref-system measurements suddenly jump.
Slow drift is determined for each Ref-system using median test. Parameters of median test can be configured by
operator.
Additionally, a bias of all Ref-system (common Bias) is determined when the Ref-system with non-zero weight is
turned off to provide continuous estimation of position.
Thus, estimation of coordinates is calculated as a weighted total of all Ref-system.
All the values of weights and bias are shown in Ref window.
8.4 Origin Ref-system
One of used Ref-system is taken as Origin Ref (see Section 8.8.3, page 148).
Ship position and velocity estimation is weighted average of all selected ref-systems filtered data.
The estimated deviation between Origin Ref and each other selected Ref-system is called "Bias".
This bias is estimated on-line and displayed in Ref Window (see figure 8.7).
If Origin Ref is failed or deselected, the system searches automatically for other Origin Ref. Preference is given to
DGPS's.
8.5 Absolute and Relative ref-systems
Ref-systems can be are absolute or relative. Absolute ref-systems allows estimating absolute ship position. Relative
ref-systems allows estimating the relative ship position only, but it's accuracy can be higher than accuracy of absolute
systems.
Absolute ref-systems
GPS is absolute ref-system. When all GPS are off, NAVIS NavDP 4000 can't determine the Origin of Coordinate
systems – Base Latitude and Base Longitude. Only Local N/E view of Map Window is available.
When the first good GGA-message from GPS is received by NAVIS NavDP 4000, the Base Latitude and Base Lon-
gitude are determined.
Relative ref-systems
HPR, Laser Radar, Taut Wire are relative ref-systems. When the first good message from transponder of relative
ref-system is received, the first measurement is interpreted as the origin of local coordinate system of this transponder.
This Origin of local system is shown in transponder table (click "Bias" heading of table to switch between "Bias/Origin"
column). Since this time, all measurements of this transponder of relative sensor will interpreted relativelly the local
system.
143
NAVIS NavDP 4000. Operation Manual
Doc. 000.JDP-10000-OME, rev.3.3.13/"2102.$–17A-Advanced"
Advertisement
Table of Contents
