CSD - Pseudo-USBL Relative Position

Pseudo-USBL System Definition

Often a dredger's PLC will output the local coordinates of a particular location as dX/dY/dZ 'offsets' from the object reference point. For example:

  • The offsets from the pontoon reference point to the center of the cutter head located on the ladder.
  • The offsets from the pontoon reference point to a point on the carrier spud.

In QINSy these offsets are interpreted as USBL observations. Hence the name 'pseudo USBL'.

Add a new system by selecting “Edit” from the menu bar, and then “New” and “System”, or right click on the item System in the item tree.

The following dialog opens. It is the first page of a wizard that steps you through the system definition process.

Enter a name you will easily recognize when Online.

Select USBL System from the drop down list.

Select a system driver from the drop down list. In addition to others there are several dredging related drivers to choose from, both serial and network. The following is a partial list:

Enter interface port parameters.

Please refer to A Note on Interfacing Parameters.

Enter a value to determine how often data will be decoded by the interface driver, i.e. the Maximum Update Rate.

Some equipment is capable of outputting data at high output rates, but it may not be necessary to use each update. A position navigation system may for example output values tens of times per second, where five times per second is sufficient. In this case, enter a value of 0.20s. Any data not decoded by the driver is lost and cannot be recovered later.

Click next to advance to the wizard's second page.

Enter parameters that define the location of the USBL transducer, which in the case of this pseudo-USBL system is the reference point from which the dX/dY/dZ values are measured.

Location 
ObjectSelect the object on which the pseudo-USBL reference point is located.
Transducer

Select the position on the object designated as the reference point for the pseudo-USBL measurements.
If the variable node is not yet defined use the sign to add a new node.
In the New Variable Node dialog enter a name for the node and the X,Y,Z offsets from the object reference point to the pseudo-USBL reference point.
This position is needed to apply heading and mounting angles to.

Reference Node

Select the position on the object for which the values output by the pseudo-USBL systems are valid.

The Reference Node of an actual USBL system is not necessarily located at the USBL transponder which is why there are two nodes to define.
With the pseudo-USBL system the 'Transducer' node is normally coincident with the Reference Node.

USBL X Y Z Data 
UnitSelect Survey unit, Meters or International feet as unit for measurements.
Sign convention for Z data 
Sign convention for Z data

From the drop down list select either positive downward (depth) or positive upward (height).
Check the sign convention used in the dredger's PLC.

Many modern USBL systems offer the ability to utilize gyro and motion sensor observations.

Also to enter the offset from the transducer to the reference point so that USBL dX/dY/dZ values as output are fully corrected for the attitude of the object and valid for a common point.
Raw corrections from either gyro or MRU are the actual readings made by the gyro and/or MRU.
The corrected readings include any fixed or variable C-O's.

Like an actual USBL system the output from this pseudo-USBL system may or may not have been corrected - check the PLC system.

Here in the system definition you do not choose which gyro or MRU observation to use. With these selections you are only determining whether such observations are to be used in Online computations.
If corrections are not applied in the system itself, it is in the Online Controller under Computation Settings that you select which gyro/MRU observations to use in correcting the pseudo-USBL dX/dY/dZ values for vessel motion.

Corrections Already Applied to Data 
RollSelect None if no roll is applied to the USBL data, select Raw VRU when roll is already applied to the data and select Corrected VRU when roll and (fixed or variable) C-O are already applied to the data.
PitchSelect None if no pitch is applied to the USBL data, select Raw VRU when pitch is already applied to the data and select Corrected VRU when pitch and (fixed or variable) C-O are already applied to the data.
HeadingSelect None if no heading is applied to the USBL data, select Raw VRU when heading is already applied to the data and select Corrected VRU when heading and (fixed or variable) C-O are already applied to the data.

Leave the box unchecked.

An actual USBL system is normally calibrated at sea and Rx (Pitch), Ry (Roll), Rz (Horizontal Alignment) alignment corrections computed. These can be entered in the USBL system itself or in the software.
These corrections are not normally applicable to a pseudo-USBL system.

Click next to advance to the wizard's third page.


Make entries for system parameters as follows:

Standard Deviations USBL Data 
TypeType of measurements from USBL: Select "Horizontal, Vertical" (rectangular) or "Angle, Range" (polar).
Typically this is "Horizontal, Vertical" for pseudo-USBL.
SD horizontally / SD anglea-priori SD is an indication of the expected variation in a measurement.
In other words, what is the error budget associated with the measurement of the dX and dY components of the pseudo-USBL observations.
In this case the magnitude depends on the measurement methods used, which can vary dredger to dredger.
Determine what sensors are being used to to measure these values. As realistically as possible estimate what the variation would be if this measurement was made 100 times.
Divide the estimated variation by four to calculate an estimated SD number.
SD vertically / SD rangeUsing the same theory as for the horizontal components, estimate the SD of dY.
Standard Deviations AlignmentA-priori SD values for the installation of the USBL transponder
SD roll offsetSD value for roll angle relative to ship's coordinate system. Usually not applicable to pseudo-USBL systems.
SD pitch offsetSD value for pitch angle relative to ship's coordinate system. Usually not applicable to pseudo-USBL systems.
SD heading offsetSD value for heading angle relative to ship's coordinate system. Usually not applicable to pseudo-USBL systems.
Sound velocity 
Used sound velocityEnter sound velocity that was set as used in the USBL device. Usually not applicable to pseudo-USBL systems.
Calibrated sound velocityEnter sound velocity value that was derived from the USBL calibration routine. Usually not applicable to pseudo-USBL systems.

None of these parameters really applicable to pseudo-USBL systems.

Corrections Already Applied to Data (Administrative)These fields have no effect on the data
Turn around delaysWhen selected enter a delay in milliseconds. Not applicable to pseudo-USBL systems.
Quality Indicators (Administrative) 
Quality indicator USBL dataSelect: "No quality info recorded", "Standard deviation", "Signal noise ratio", "System specific" or "Subjective scale".
Perhaps useful to record.
Quality indicator descriptionsEnter the remarks for these parameters. Only possible when one of the Quality Indicators was selected.

Press <Next> to advance to the wizard's fourth page.

USBL targets are the other end of the dX/dY/dZ measurements that originate at the USBL reference point.

For example the reference point of the primary vessel (pontoon) is also the reference point for the pseudo-USBL system. A dX/dY/dZ measurement is made FROM this reference point TO the the center of the cutter head.
Once targets have been added, this window shows a list of targets (located on nodes) and Slot identification numbers:

Begin by using the Add button to display a list of available nodes on which the 'target' might be located. The image shows that two nodes have already been selected as targets so neither is shown in the list. If a third target is required its associated node would be one of those shown listed, or, if not listed, a new node can be created.

Selected USBL Targets 
Add

Opens the Select Node dialog window used to add new nodes.
This can be a variable node (located on an object) or a fixed node (located in earth coordinates).
Select an existing node from the list or use the Add button:
to add a new variable node.
to add a new fixed node.

RemoveSelect a node in the list and remove this from the USBL system.

Targets in a real USBL system are each assigned a unique identification called a Slot Id in QINSy.

This ID is written into the data message so that when decoding message strings the software can differentiate target 'A' data from target 'B' data.

A pseudo-USBL employs the same concept. If the PLC outputs dX/dY/dZ data from multiple 'targets', each will have a unique identifier. That identifier must be associated with the correct node.

Selected USBL Targets 
Edit

Once the node has been added click on Edit to open the Edit Slots window.
Enter the identification slot number.

Not really pertinent to psudo-USBL but something to be aware of: some drivers expect either a "B" or "n", where n is the slot id.
Example: slot 3 = B3 or B03 or 03. If only the number 3 is entered no data may be received.

Press Finish to complete the pseudo-USBL definition.

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