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.
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.
|Object||Select the object on which the pseudo-USBL reference point is located.|
Select the position on the object designated as the reference point for the pseudo-USBL measurements.
Select the position on the object for which the values output by the pseudo-USBL systems are valid.
|USBL X Y Z Data|
|Unit||Select 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).
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.
|Corrections Already Applied to Data|
|Roll||Select 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.|
|Pitch||Select 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.|
|Heading||Select 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|
|Type||Type of measurements from USBL: Select "Horizontal, Vertical" (rectangular) or "Angle, Range" (polar).|
Typically this is "Horizontal, Vertical" for pseudo-USBL.
|SD horizontally / SD angle||a-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 range||Using the same theory as for the horizontal components, estimate the SD of dY.|
|Standard Deviations Alignment||A-priori SD values for the installation of the USBL transponder|
|SD roll offset||SD value for roll angle relative to ship's coordinate system. Usually not applicable to pseudo-USBL systems.|
|SD pitch offset||SD value for pitch angle relative to ship's coordinate system. Usually not applicable to pseudo-USBL systems.|
|SD heading offset||SD value for heading angle relative to ship's coordinate system. Usually not applicable to pseudo-USBL systems.|
|Used sound velocity||Enter sound velocity that was set as used in the USBL device. Usually not applicable to pseudo-USBL systems.|
|Calibrated sound velocity||Enter 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 delays||When selected enter a delay in milliseconds. Not applicable to pseudo-USBL systems.|
|Quality Indicators (Administrative)|
|Quality indicator USBL data||Select: "No quality info recorded", "Standard deviation", "Signal noise ratio", "System specific" or "Subjective scale".|
Perhaps useful to record.
|Quality indicator descriptions||Enter 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|
Opens the Select Node dialog window used to add new nodes.
|Remove||Select 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|
Once the node has been added click on Edit to open the Edit Slots window.
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.
Press Finish to complete the pseudo-USBL definition.
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