The Sonar Viewer

The sonar viewer is capable of displaying Lowrance or Simrad sonar log files with the file extensions .SLG, .SL2 and .SL3.


Loading Sonar Log Files

To load a sonar log file, choose the required file using the FILE/Open screen - see Loading and Saving Files. Note that only one sonar log file can be open at any time - any previously loaded sonar log file will be replaced in the sonar viewer when another one is loaded.


Sonar Index Files, and Importing Sonar Log Files from Removable Drives

When loading a sonar file for the first time, the full file must be read by the Waypoint Manager, and an index file created. This can be a time-consuming process, but subsequent loading of the same log file which be much faster.


To improve performance when displaying sonar logs, the Waypoint Manager creates a sonar log index file in the same location as the existing log file, with name <existing_sonar_log_filename>.IDX. In order to create this file, the disk location for the sonar log file must be writeable.

For performance reasons, sonar log files should always be read from a local hard drive, and never from a USB stick or SD card. For this reason, new sonar log file recordings should be copied to a local drive before being open for viewing in the Waypoint Manager.


Arranging the Sonar and Map View Displays

When a sonar log file has finished loading, the Sonar Viewer display is added to the main display area as a separate, tabbed window. Click on the Sonar View tab to display the sonar view, and on the Map View tab to return to the map view. The main display can be split, so that both the map and sonar views are visible together - see Arranging Sonar And Map Views for details on how to do this.


The Sonar View

The Sonar View window is split into separate panels, one for each available channel, with a control bar underneath for controlling sonar playback, horizontal zoom and file position.

A data panel at the top of the sonar view shows data relating to the current position in the sonar log file, including location, speed, heading and depth.

When a sonar log file is loaded, a trail is created that describes the route of the sonar log. The current position of the sonar log is represented with a small boat icon over the trail in the map view.



Playback Control

A control bar underneath the main sonar display contains controls for sonar playback, position and horizontal zoom:



Play/Pause and Speed Control

Click the play/pause button (1) to start or pause sonar playback. Speed of playback can be adjusted by using the slider (2), between a range of 1x (real time) to 30x. The current time position within the file is shown (3). Note that the displayed time relates to the leading edge of the sonar image, and so will never show zero.


Horizontal scale (vertical, for sidescan) controls the scale along time time axis. Move the slider (4) left to reduce the scale, and right to increase the scale (and effectively zoom in).


The position within the sonar log can be controlled directly be using the scroll bar (5), and also by dragging within the sonar view with the mouse mode in pan mode.


Individual Sonar Channel Displays

Each individual sonar channel can be configured by controlling the selected palette, brightness, contrast and zoom level.

The same mouse modes and actions can be applied within the sonar view as in the map view:


Zoom in or out by using the mouse wheel. Note that mouse-wheel zooming in the sonar view zooms along both vertical and time axes together. To zoom in one axis only, use the horizontal zoom bar in the playback control bar (see above), or use the vertical zoom control in the channel control panel (see below).

Double-click to fit to vertical (or horiztonal, for sidescan) limits.

Pan the sonar image horizontally or vertically by using the mouse in pan mode, or by using the middle mouse button.

Distance can be measured, and object height estimated in the sidescan view, with the mouse in measure mode (see below).

Waypoints can be created within the sonar view by left-clicking with the mouse in drop waypoint mode, or via the right-click menu.

The relative size of each sonar channel can be adjusted by clicking and  dragging the white dividing bars between them with the left mouse button.


Showing, Hiding and Arranging Channels

The visibility of individual sonar channels can be toggled, and the positions of channels within the sonar view grid can be arranged.


To toggle visibility of a channel, click on the Show/Hide button for the required channel in the SONAR channels menu bar, or click within one of the channel buttons inside the channel selector pop-up, that becomes visible when the mouse pointer is held towards the bottom-right corner of the sonar view:




To rearrange the channel layout, click and drag a sonar channel in the channel selector pop-up to the required location, with the left mouse button. In the example below, the downscan channel has been repositioned above the sidescan channel:




Colour palette, Brightness and Contrast

Colour palette, brightness and contrast can be controlled via the SONAR menu bar, or via pop-up controls in each of the separate channel display panels. To see a pop-up channel control, hold the mouse pointer towards the bottom/left corner of a channel display:




Brightness (1), Contrast (2) and Palette Selector (3). Vertical range can be adjusted by using the slider at the right (4). Drag the top bar to adjust the upper limit, and the lower bar to adjust the lower limit.



Equivalent controls can be found in the SONAR menu bar (2). Note that in the SONAR menu bar, controls are only shown for one channel at a time. To select the "active" channel, click within either the mini-channel display within the menu bar (1), or anywhere within the required channel in main sonar display.


The Fit Height (Fit Width for sidescan channels) button adjusts the displayed vertical (or horizontal, for sidescan) limits so that they fit the available screen space. This function is also available via double-clicking within the sonar channel display.


Autogain for Sidescan Channels

An extra setting, autogain, is available for the sidescan channel only. Autogain adjusts side-scan signal returns to equalise the brightness across the sidescan swath. The amount of autogain applied to the sidescan display can be adjusted using the slider; move the slider all the way to the left to remove auto-gain completely, and all the way to the right for full auto-gain.



Additional Options


Show Data Panel  toggles the visibility of the data panel at the top of the sonar view, which contains information about location, heading and speed at the current position within the sonar log file.

Show Depth Scale toggles visibility of the depth/distance scales in the individual channel views. Note that this setting applies to all visible channels.

Sample Mode refers to the way that sonar imagery is rendered. Sonar imagery can be drawn "smoothed", where individual sonar return "pixels" are blended with their neighbours, or "raw", where each individual sonar return is rendered as a sharply defined pixel. Differences between the two modes are more readily observed at higher zoom levels.

Swap Sidescan Sides can be used to swap the port and starboard channel positions. This function can be required when the sidescan transducer has been mounted backwards.

Take Snapshot copies the current sonar view to the clipboard as a high resolution image. Images from the clipboard can be pasted into other applications, such as email or word processing applications.

Save Settings as Default saves the current sonar palette, brightness and contrast settings, for use as the default settings the next time a sonar log file is loaded. Note that, by default, settings are persisted on a per-file basis, and will be restored the next time that file is loaded. Default settings are only applied to sonar log files that are loaded for the first time.



Measuring Distance and Estimating Object Height

Measuring Distance

With the mouse in measure mode, distances can be measured within any sonar channel display by holding down the left mouse button and moving the mouse over the required area:





Measuring height

In sidescan channels, the height of an object can be estimated by measuring its shadow.

To estimate an object height, click and hold the right mouse button and draw a line for the full length of the object shadow.


This tree stump is approximately 1.9m high


The measure tool can also be used to estimate the depth of objects within the water column (e.g. fish). In this case, the tool should be extended from the object to the shadow cast by the object. The height shown will be the height of the object from the bottom, and the depth of the object can be calculated by subtracting that height from the current depth.