About lines

A line in Echoview is defined by a series of measurement vs. time coordinates and is displayed on an echogram by drawing line segments between adjacent coordinate points.

Lines are variables and:

are stored as data (depth vs. time coordinates, or range vs. time coordinates for sounder-detected bottom raw lines) or as a formula (a function of another line).
In the former case you may be able to edit the coordinate data (see below) in the latter case you can edit the formula.
have coordinate points that have a positive or negative depth (i.e., be below or above water).
are displayed as a series of line segments. Upon the creation of editable and virtual lines, line status is assigned to line segments. The line status applies to the coordinate point at the left of the line segment. Also, you are able to manually assign line status.

On echograms:

The active line is drawn with a thickness of two pixels.
Lines are drawn in line status colors with a line thickness. Line status colors and thickness may be specified for all lines in an EV file or for a particular line variable.
The name of a line can be seen by pointing to it with the mouse - it will be displayed on a tooltip.

Lines can also be managed on the Dataflow window.

You can create any number of lines in an EV file.

When a new EV file is created, there is no default line. A new line must be created and made active before you can edit it or run a line pick. If a data file includes the bottom depth for a ping (for one or more variables), a sounder-detected bottom line is created for each of those variables.

All lines except sounder-detected bottom lines are available to every acoustic variable in an EV file. However, you can choose to set a line to be 'not visible' for a particular variable (on the Lines page of the Variable Properties dialog box).

The active line

An active editable line can be selected by:

choosing a line from the drop down list on the Line and Surface tool
the Lines page of the Variable Properties dialog box
double-clicking a line on the echogram to select it as the active line

Inactive lines are displayed with a width of one pixel. The active line is the line that will be edited when you choose to change the line status, or use the Line and Surface tool to edit. The active line is bulleted on the Line and Surface tool list.

At any point in time, only the active line is editable.

Notes:

If no active line is set on an echogram the Set Active line dialog box will open when you choose to change the line status or try to use the Line and Surface tool.
Raw and virtual lines can't be set as active lines.

Lines are described in detail in the following sections:

Line types
- Raw
- Editable
- Virtual
- Breaks in lines
Line properties
Line pick
Uses for lines

Line types

Editable lines

All lines other than virtual lines and raw lines are editable lines. Editable lines are displayed as solid lines. They are stored as a series of depth vs. time coordinates. Editable lines can be created, edited, deleted, and set as the active line on an echogram. You can also choose to extend editable lines during live viewing or modify sections of editable lines.

Editable lines are created in the New Editable Line dialog box or are drawn using the left mouse button.

To display a line as a graph, on the Dataflow window select a line object, right-click and select Graph.

Raw lines

Raw line data may be read from a data file. Raw lines include sounder detected bottom lines, depth lines (recorded by depth sensors) and heave lines (recorded by heave sensors). Raw lines are associated with a transducer. They cannot be edited or deleted, although they can be made 'not visible' (on the Lines page of the Variable Properties dialog box).

Sounder detected bottom lines are stored as range vs. time coordinates, not depth vs. time coordinates as other lines are. There will maximally be one such coordinate pair for each ping (all points on sounder-detected bottom lines coincide in time with pings). Sounder detected bottom lines have a Calibration page on the Line Properties dialog box which enables the conversion of range to depth for echogram display and other line handling. Sounder detected bottom lines are affected by changes to transducer geometry and are adjusted by a SoundSpeedProfile. See also: Note for the visibility of sounder-detected lines.

Raw depth and raw heave lines are stored as depth vs. time coordinates.

You cannot edit raw lines. You can however, create new (and identical) editable lines based on the raw line, edit that line and use it in place of the raw line. The new editable line will be available to all other variables. A virtual line based on a raw line may also be useful.

Notes:

A line GPGGA variable can represent altitude data from a GPS antenna.
Prior to Echoview 5.4, sounder-detected bottom lines were associated with an acoustic variable. Post Echoview 5.4, EV files, created in earlier versions, will associate such lines with the transducer for the Sv variable. This is likely to be correct in many cases. But it is advisable to verify if it is the correct transducer to use. Identified issues/mismatches from this process are flagged in the Messages dialog box.
Sounder-detected bottom lines that do not contain any data are defined as unavailable on the Dataflow window.

Virtual lines

Virtual lines are created in the New Virtual Line dialog box. Line operators, including those that perform line pick, are automatically listed in this dialog box.

Virtual lines cannot be edited (by the Line and Surface tool) but the formula defining them can be edited (on the Line properties dialog box).

You might for example pick a bottom line, then define a virtual line 5m above it. If you edit or re-pick the bottom line, the virtual line will be affected as well, remaining a consistent 5m above the altered bottom line.

You can change the appearance of virtual lines on the Display page of the Line properties dialog box.

Note: While you cannot edit virtual lines directly, you can create a new (and identical) editable line based on the virtual line and edit that. This new line will not be a virtual line and will not respond to changes in the virtual line dynamically.

Operators that create virtual lines are:

Breaks in lines

Echoview's representation of 'breaks' in lines is different under editable lines and virtual lines. A break in a line means the line segment is not displayed on the echogram. A line segment is checked at both its line points. A break may arise from invalid depth, no data or a line status value of None.

Breaks in editable lines are stored in a shortened manner. Breaks in virtual lines are stored in an unshortened manner. This difference affects both echogram display and exported data.

Line Properties

Line settings which can be viewed on the Line Properties dialog box. The line type affects the pages available under the Line Properties dialog box.

Note: The settings in the Line properties dialog box only apply when either new data is added (e.g. by live viewing) or if a section of the line is directed to be recalculated (by Shortcut menu > Recalculate Line).

To view or edit Line properties:

for the active line, on the Echogram tools toolbar, click the Line and Surface tool arrow and then click Line Properties.
select a Line on the Dataflow window then click Line Properties on the Shortcut (right-click) menu.
for a line on an echogram under the mouse pointer, on the Shortcut (right-click) menu click Line Properties.

Calibration

Sounder-detection bottom lines use calibration settings.

Be aware that changes to calibration settings, that are used in range calculations, may shift ping data in the depth dimension but will not automatically adjust the position of existing regions and lines. You should review any existing regions and lines to ensure they are still valid.

For more information refer to Range calculation effects on regions and lines.

Color, gaps

Line status colors and thickness for all lines in an EV file may be changed under the Line display defaults section of the Echogram page of the EV File Properties dialog box.
Line status colors and thickness for a particular line may be changed under the Display page of the Line Properties dialog box.
Line colors are changed by altering the color scheme on the Display page of the Variable Properties dialog box.
You can find gaps in lines using the line-break finding tool, or make a copy of a line with all gaps bridged using the Span gaps setting on the New Editable Line dialog box.

Note: Echoview may automatically adjust the Line color on graphs and echograms to improve the contrast between the line and background.

Visibility

Toggle the line visibility to show or hide the line on echograms. Echoview automatically sets and keeps lines that are being used by a variable (e.g., as an exclusion line) as visible.

You can toggle the line visibility from the Visibility page of the Line Properties dialog box, or the Variable Properties dialog box for an operator. In the latter case, you typically toggle the visibility from the Lines page. However, lines selected for use in these operators will always be visible

Attenuated signal removal
Deadzone estimation
Line bitmap
Transient noise sample removal
the single target detection operators (refer to the list on the Single target detection algorithms page)

Lines depths, relative to zero meters at the water surface, are positive below the water and negative above the water. To display lines above the water adjust the Echogram display limits.

Note: Sounder-detected lines are set automatically to be the Analysis Exclude below line on the raw variable, To change the visibility of a sounder-detected line, first set the Exclude below line to None.

See also:

Change the settings of an existing line.

Line pick

For editable lines, the line picking algorithm is configured under Single beam tab on the Lines and Surfaces page of the EV File Properties dialog box.

For virtual lines, the line picking algorithm for a Line pick operator is configured on the operator specific page of the Line Properties dialog box.

See also: Line picking.

Uses for lines

Lines are used to represent:

the bottom
the lower limit of surface noise
other linear or bathymetric features on an echogram

For example, different lines could be created to represent the depth of the sea, river or lake bed (depth of maximum backscatter), the acoustic bottom (depth of backscatter from bottom, at a defined level) and/or the second bottom (maximum return from second bottom reflection).

Line-referenced echogram
Exclude-above, Exclude below
Grid reference-line
Line status
Line export
Line-relative regions
Find Next/Previous integram value
Other ways to view lines
Import, Copy/Paste
COM

Line-referenced echogram

A line-referenced echogram displays echogram samples, regions, lines and grids relative to a specified Echogram reference line and is a display-only feature. The reference line can be any Echoview line. A line-referenced perspective may be useful during bottom line verification or while observing features in the water column.

A line-referenced echogram:

allows the use of the Tape measure tool
allows the use of line editing and line pick, even on the reference line
responds to Mouse pointer duplication
responds to the right-click menu, Synchronize and Synchronize to Point
doesn't allow onscreen integration, new region creation or existing region edits

Notes:

To view all data on line-referenced echograms you may need to use Manually set the display limits.
An echogram with numerous regions or lines may respond more slowly than expected; this type of display uses extra computations for regions and lines.
Under this display, existing lines may display additional line segments to accommodate the change in (reference line) perspective.

Exclude-above and Exclude-below lines

When analyzing or integrating echogram data, lines can be selected to define the upper and lower depth limits of data points to be included in calculations. These are termed the exclude-above and exclude-below lines.

Exclude-above and Exclude-below lines are set on the Analysis page of the Variable Properties dialog box. See also the Near-field depth estimation virtual line and its use as an exclude above line.

Export variables

You can output optional line-related variables with analysis exports. Analysis Domain variables include:

Line usage

Use Shortcut menu View Properties on the Dataflow window to display Line usage relationships (active, analysis, exclude-above and exclude-below) between variables and lines.

Grid line-reference

Cell integration and other analysis results and can be calculated relative to a Grid reference-line. Layers are numbered relative to the specified reference-line.

An editable or virtual line can be used as a reference-line for the horizontal grid of an echogram.

Note: A hidden line becomes visible when it is selected as a grid reference-line.

Export variables

You can output optional line-related variables with analysis exports. Analysis Domain variables include:

Line status

Line status can be used in a number of ways to record information or influence analyses.

The line status can be set using the Shortcut (right-click) menu on an echogram when a selection is made.

Line export

Echoview supports the export of line data under four distinct file formats.

Two easily edited CSV line file formats can be added to a fileset to derive raw line variables.
The EVL line file format can be imported as an editable line variable.
The EVD line file format is XML based and can be added to a fileset to derive a raw line variable.

Line-relative regions

Regions can be defined using lines to mark the upper and lower boundaries. Although referred to as "line-relative regions" in Echoview, these regions are identical to other regions. The term "line-relative" refers only to the method of creation.

Line-relative regions are used to:

create "bottom referenced layers" or analysis regions, that are a constant height above the bottom.
define a region to integrate the second bottom, for bottom classification studies.
estimate acoustic deadzone volume, by defining a region between the acoustic bottom and the depth of maximum backscatter.

A line-relative region is not dynamically linked to a line. If you edit the line(s) relative to which the region was defined you may need to redefine the region.

Find Next/Previous integram value

Use lines to constrain an integram Sv analysis. Refer to About the integram and Using the integram for more information.

Other ways to view lines

A line may be viewed as a graph or in a table.

Import, Copy/Paste

Both virtual variables and line variables are included under Import Virtual Variables (.ev).

Line variables may be included in the Copy/Paste of a virtual variable chain. Lines may be discrete objects in the chain or be a selected line within the Variable Properties of another variable. For missing lines, affected settings are set to None. For unavailable lines (grey), such lines can be reconnected in the dataflow window or changed via the Variable Properties of an affected variable.

COM support

COM support for lines includes:

EvFile.Lines and EvLinesCollection
EvLine