Line picking and bottom detection

This page covers:

• Line picking on single beam echograms

• Bottom detection on multibeam echograms

Line picking on single beam echograms

Line picking is the process of picking lines from acoustic variables using algorithms. This is typically done to detect bottom lines in variables.

Before you pick an editable line, you should access the Line Pick page of the EV File Properties dialog box and check the line picking algorithm and other settings that will affect line picking.

To pick an editable line over the entire variable:

1. Display a single beam echogram
2. Click the Line draw tool  , then click New Editable Line
3. Select the Line pick from current variable option
4. Select Create new line and enter a name for the line
   - OR -
   Select Overwrite existing line and select a line to overwrite
5. Click OK

To replace part of an existing line by applying a line picking algorithm to the data in a selection:

1. Display a single beam echogram.
2. Click the Line draw tool , then click the required line to make it the active line.
3. Make a selection using one of the echogram selection tools.
4. On the Shortcut menu (right-click), click Pick Line.

To pick a virtual line:

1. Select a Line pick operator when you follow the instructions to create a virtual line.

Notes:

• If there is high surface noise on the echogram the Line pick algorithm may not pick the bottom as you would expect. If this is the case, you will get better results by setting the Start depth and Stop depth on the Line Pick page of the EV File Properties dialog box.
• If there are breaks in the bottom return the line pick may look irregular. You can use the Line draw tool to edit these parts of the line pick. Alternatively, you can delete parts of the line by setting the Line status to None for selected areas.

See Line picking algorithms and Best bottom candidate settings for more detailed information.

Bottom detection on multibeam echograms

A bottom can be detected on acoustic multibeam variables. Bottom detection is performed using the settings on the Multibeam Bottom Detection Properties_dialog_box applied to the Multibeam bottom detection algorithm. A bottom detection on multibeam data produces a surface.

To display a preview of the detected multibeam bottom:

1. Display a multibeam magnitude beamformed echogram.
2. On Echogram menu, click Variable Properties.
3. Click the Display tab.
4. In the Multibeam display section, select the Show multibeam bottom preview check box.

To detect a multibeam bottom:

1. Display a multibeam magnitude beamformed echogram.
2. On Echogram menu, click Create 3D Object, then click Bottom surface
3. On the Detect Bottom Surface dialog box, enter a name for the surface and enter other settings as required.
4. Click Detect.
5. To view the surface you may either,
   1. add it to a scene, or
   2. view its intersection with the current echogram.

Notes:

• You can only detect a 3D bottom surface if GPS data are available.
• Each surface has its own 3D Object Properties dialog box where the name and appearance can be edited and details about the 3D object are available.
• To view the surface you will need to add it to a scene, see About the Scene window.
• You can resample a 3D bottom surface with a different resolution using the Resample Surface dialog box available from the Scene Manager.
• If the detected bottom surface appears unusual please refer to known 3D surface detection problems.

See also

Line picking algorithms
Multibeam bottom detection algorithm
Creating, renaming and deleting lines
About setting variable properties
Best bottom candidate description of settings

Echoview Help file 5.2.21 for Echoview 5.2.55 Monday 21st May 2012

Please report any errors or omissions to support@echoview.com.