Detect 3D Schools dialog box
The Detect 3D Schools dialog box is used to enter the settings that will be used to create 3D regions.
To invoke the Detect 3D Schools dialog box:
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Display a multibeam echogram.
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On the Echogram menu, click Detect Schools.
The Detect 3D schools dialog box contains four pages:
Note: The Exclusion page and Size criteria page in the Detect 3D Schools dialog box are dynamically linked to pages of the same name in the 3D Schools Detection Properties dialog box, i.e. changes made to a page in one dialog box will automatically be applied to the same page in the other dialog box.
Data page
The Data page of the Detect 3D schools dialog box contains the following settings:
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Settings
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Description
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First ping
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Enter the range of pings to be included in the detection.
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Last ping
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Algorithm
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Choose the Detection algorithm.
The Detection algorithms available are a function of the ping mode of the variable:
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Detection algorithm
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Ping mode
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Cruise scanning
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By ping
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Instrument scanning
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2 (Multibeam)
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Y
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Y
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N
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3 (H-mode)
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Y
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Y
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Y
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4 (V-mode)
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Y
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Y
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Y
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5 (S-mode)
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Y
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Y
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N
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Region width
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Used to select the region width in meters when the By ping detection algorithm is selected.
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3D Regions page
The 3D regions page of the Detect 3D schools dialog box contains the following settings:
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Settings
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Description
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Assign class
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Select a region class to assign to the 3D regions created by schools detection.
Note: If you want to define a new region class, use the Classes page of the EV File Properties dialog box before you configure the parameters for a 3D schools detection.
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Delete 3D regions with this class first
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Select this to delete 3D regions of this class before the detection.
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Save vacuoles
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Select this to save any detected vacuoles with each created 3D region.
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Exclusion page
The Exclusion page of the Detect 3D schools dialog box is used to eliminate data from the detection process. The settings on this page are applied to each multibeam ping.
Under Bottom elimination choose one of the options:
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Settings
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Description
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None
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Choose this option if you do not want to eliminate bottom data or there is no bottom data in the echogram
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Specified maximum range
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Choose this option if you want to exclude data outside a specific range. Enter the range in meters
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Exclude below surface
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Choose this option if you want to exclude data below a surface.
Under Surface choose which surface to use. You may want to see the intersection of that surface with this ping to see what will be excluded.
Enter an Offset depth value in meters to add an offset to the surface depth (recommended). The surface is effectively moved by this offset for the purposes of exclusion.
Click Exclude beyond minimum surface range to exclude all samples beyond the range R where R is the range to the nearest point (to the transducer) on the surface-ping intersection. This is effectively the same a selecting Specified maximum range above and entering the range R. This feature is intended to help remove the bottom echo trace sometimes visible in multibeam echograms beyond the range R (an artifact introduced in the beam forming process).
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And/or, exclude data near the transducer using this option:
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Setting
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Description
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Exclude before specified minimum range
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Enter a range in meters and choose this option to exclude data from the transducer up to the specified range.
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Size Criteria page
The Size criteria page of the Detect 3D schools dialog box is used to control the minimum dimensions of the 3D regions and vacuoles respectively.
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Settings
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Description
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Minimum longest dimension
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Define the minimum dimensions (in meters) for an individual school or vacuole.
Any schools that are smaller than these dimensions will be discarded during the 3D schools detection process.
The Minimum dimensions reflect the order of the distance between pings; this depends on the cruising speed and ping interval. Initial values could be 30, 20 and 10 respectively.
A 3D object's bounding box is a 3D object metric and can be displayed in a scene or the values of its dimensions and orientation can be viewed in the Further information box of the General page of the 3D Object Properties dialog box.
Note: The dimensions of the bounding box are aligned with the 3D object.
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Minimum middle dimension
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Minimum shortest dimension
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Warning: 3D schools detection can be very slow (taking hours on even a fast machine) and requires large amounts of RAM. This is particularly true if the minimum 3D size limits are smaller than or near to the size of individual data samples, which means that schools containing a very small number of samples will be considered during the processing. If you find that detection is slow, does not complete in a reasonable amount of time or reports running out of memory, then consider:
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increasing the minimum dimensions on the Size Criteria page
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segmenting the EV file into smaller ping ranges (say 250 pings in each range) and doing separate detections for each range
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increasing the physical RAM in your computer to 1Gb or more.
Notes:
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the detected school position, size and shape include transducer geometry effects.
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To view 3D regions you will need to add it to a scene, see About the Scene window.
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Each 3D Region has its own 3D Object Properties dialog box where its name and appearance can be edited and details about the 3D object are available.
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You can view the details of the vacuole(s) in a 3D region or delete a vacuole from a 3D region, on the Vacuoles page of the 3D Object Properties dialog box.
See also
About 3D schools detection
About Scenes
Using scenes
About 3D objects
Creating 3D Objects
About Surfaces
3D Schools Detection Properties dialog box
3D object problems
Preparing instrument scanning data for schools detection