Sidescan Mosaic Track Review

Sidescan Track Review

Sidescan track review extends the existing track edit window to display in-place sidescan sonar imagery for any track that contains sidescan data.

The track edit window provides a convenient and fast way to review sidescan sonar imagery from a single sonar log and perform actions such as marking waypoints on underwater structure, exporting selected regions as high-resolution images, and selecting regions of sidescan to be added to a sidescan mosaic.

Displaying Sidescan in the Track Edit Window

·Open a track for editing by double-clicking the track in the Asset Library or Global View. The track will be displayed as a series of depth points.

·If the selected has track has associated side-scan data, the Show Sidescan button will be enabled (circled).

·Clicking the Show Sidescan button will replace the depth point view with the sidescan view (clicking the Show Sidescan button again will revert the track display to the track-point view):

·Sidescan imagery is displayed (or the sidescan coverage area, depending on the current zoom level).

·The Sidescan Swath Control (circled) is also shown at the bottom of the track edit area.

Sidescan range display and sidescan imagery display

Below certain zoom levels, sidescan imagery is not displayed in the track edit window. Instead, a simple shaded polygon is drawn that shows the sidescan coverage for the track. This is for performance reasons; since sidescan data is loaded and processed directly from the sonar log file as required, it is not practical to display to display the full sidescan imagery for very large sections of data.

·If the track is displayed at too low a zoom level to show imagery, zoom in on an area of interest until the imagery is displayed:

When sidescan imagery is displayed in the track edit window, the window operates in the same was as any other ReefMaster edit window. The view can be zoomed and panned, measurements can be made using the ruler tool and waypoints can be added and edited.

Controlling the sidescan display

By default, the entire sidescan swath is selected for display and can be viewed by simply panning the track display area (by using the mouse grab tool, or the middle mouse button, which can be used regardless of the current mouse mode).

The displayed sidescan can be controlled in a number of ways:

·Start and end positions can be adjusted to limit the length of the displayed swath.

·Port and starboard ranges can be adjusted to limit the width of the swath. Both the upper and lower ranges for each swath side can be adjusted.

·Brightness and contrast can be adjusted, and the Auto-gain function can be turned on and off.

·The displayed portions of the swath can be limited according to Maximum Curve Radius and Maximum Speed.

·The opacity (transparency) of the swath can be adjusted.

·The palette can be selected.

Swath start and end positions

Swath start and end positions can be controlled using the Sidescan Swath Control bar, located at the bottom of the track edit window (note: this control bar is only visible when the track is in Show Sidescan mode).

The Sidescan Swath Control

The start and end positions of the displayed swath can be adjusted by dragging the sliders (3) and (1) with the mouse, using the left mouse button. When the displayed range is less than the full range of the track, the entire displayed range can be moved by dragging the range bar (2). Clicking in the areas to the left or right of the range bar will move the entire range by a small amount towards the direction of the click. To reset the range to full, click the Full Range button to the right of the toolbar (5).

Keeping the active swath region centred

The Keep Centred button (4) acts to keep the front edge of the visible swath in the centre of the edit window. This feature is very useful when reviewing tracks at a high zoom level, as the swath is always kept in view. A track can be reviewed very quickly by selecting the Keep Centred option and dragging either the front edge of the swath, or a small swath range, from the beginning to the end of the track. An advantage of using this technique is that later portions of the swath do not overwrite the images at the current position.

Tips for reviewing tracks

The single most effective tool for efficient sidescan sonar review is the swath range slider coupled with the Keep Centred option.

To review a track using this method:

·Click the Keep Centred button at the left of the sidescan swath control. The screen will centre itself on the leading edge of the visible swath.

·Move the end of the visible swath to a position near the beginning of the track. The end of the swath position can be adjusted by dragging the right-hand slider of the Sidescan Swath Control to the left.

·Once the selected range is at the length you want, simply drag the whole range towards the end of the track (to the right). The visible portion of the swath will move along with the slider, and the screen will keep centred on the range.

The image below shows an example of a track being reviewed in this way. In this particular area of the track, the swath overwrites itself several times. By limiting the visible range of the swath, we can review all of the recorded sonar and possibly see things that would otherwise get overwritten:

Playback using the sonar viewer

During sonar playback, the screen remains centred on the current sonar position if the Show Boat Position option has been selected in the sonar viewer (circled in the image below). We can use this feature to review sidescan data in a track:

·Open the sonar viewer panel by clicking the Show Sonar button (circled, left of screen, in image below).

·Ensure that the full sidescan swath is visible by clicking the Full Range button at the right of the Sidescan Swath Control.

·Start playback of the sonar recording. The sonar recording will commence playback, and the track view will update to keep the current sonar position in the centre of the screen.

·The position of the playback can be adjusted at any time, either by dragging the sonar position slider, or grabbing the sonar image in the sonar viewer with the mouse in Pan mode (see the sonar viewer manual pages for more information). Adjusting the position of the sonar in this way will also update the position in the track edit area.

Playback using the sonar viewer is a useful technique, especially if it is important to be able to view associated conventional or down-scan sonar with reference to sidescan in the same location. This method is less useful where tracks have a large number of overlapping sections, as later sections may overwrite and obscure earlier parts of the swath. Also note that displaying sidescan required a lot of processing power, and higher speed sonar playbacks may start to lag.

The Sidescan Properties Panel

All sidescan properties, other than the swath limits described above, are available in the Sidescan Properties Panel and the sidescan swath Context Menu (see below).

The sidescan properties panel is located in the Edit panel at the right of the window, under the Sidescan expander. The edit panel can be displayed by clicking on the Edit tab (see application layout for more information):

(1) Palette selector (properties panel only)

Any RGB colour palette can be used for the sidescan display, see the palette editor manual page for details on how to create a custom palette. When the track display is in sidescan mode, the palette selector button in the display-area toolbar can also be used to select the sidescan palette.

(2) Auto-gain on/off

The auto-gain function evens out the signal return across the full sonar range. This can reveal details at the edges of the sonar range that would otherwise be hard to see. See the sonar viewer manual page for more information.

(3, 4) Port and Starboard ranges

The upper and lower limits for the port and starboard sonar can be adjusted by using the port and starboard range sliders, which are available in the sidescan context (right-button) menu and the Sidescan Properties panel. The port and starboard range sliders work in a similar way to the swath position slider described above; either edge of the slider can be adjusted independently to move the upper or lower range, and the whole range can be moved by dragging the centre of the range slider. The range can be restored to its full extent by clicking the Full Range button to the right of the slider.

Adjusting the lower limits of the port and starboard ranges can be very useful when viewing areas of track with significant overlap. In the example below (left), low quality data at the extreme of the sonar range is obscuring overlapping sections of better quality imagery. The image on the right is the same section of track with the port and starboard ranges reduced:

Adjusting the port and starboard ranges is also a very useful technique when arranging multiple sonar track "segments" in a Sidescan Mosaic.

(5, 6, 7) Opacity, brightness and contrast

Transparency, brightness and contrast can be adjusted using the sliders.

(8, 9) Minimum curve radius and maximum speed filters

The quality of the source data makes a huge difference to the results that can be achieved using the ReefMaster sidescan mosaic functions.

Data recorded during tight turns, or at too high a boat speed, is often particularly poor quality. Tight turns mean that an excessive amount of interpolation is required on the outside of bends, and recordings made at too high a speed are often very noisy.

ReefMaster provides simple filters that can be used to hide data below certain curve radii or above a specified speed threshold. Note that in the track-review window, all filter actions are completely non-destructive.

Minimum Curve Radius

The curve radius of a track section is defined by the radius of the circle that would be formed if the current rate of turn was completed for a full 360 degrees. Note that the curve radius is calculated for the centre of the track, not the edges of the sidescan range:

The minimum curve radius can be specified to a distance between 0 and 100m (328 feet) by using the slider available in either the Sidescan Properties Panel or the Sidescan Context Menu. Applying a minimum curve radius filter to a sonar track hides all sonar data from sections of the track which have a smaller curve radius than the distance specified:

Setting a minimum curve radius removes tight turns from the sidescan display

Maximum Speed Filter

The maximum speed filter removes sections of track where the boat speed is above the specified maximum speed, which is shown in knots or km/ph, depending on the current speed units setting. When the maximum speed is set to zero, no maximum speed filter is applied. Hence as the slider is moved upwards from 0, progressively more sonar will be displayed. To remove the maximum speed filter, return the slider to the zero position.

The sidescan swath context menu

The sidescan context menu can be shown by clicking the right mouse button when the mouse pointer is held over the edge of the sidescan swath. The outline of the swath changes to red when the mouse pointer is held over it, which indicates that the sidescan swath is the current "object of interest" within the reefmaster view.

The sidescan context menu contains most of the same options as those presented in the Sidescan Properties Panel, with the exception of the palette selector, and the addition of the Add to Mosaic function:

Add to Mosaic

The Add to Mosaic function adds the currently range of the sidescan swath to a Sidescan Mosaic, where it can be combined with other sonar data. See Sidescan Mosaicking for more details.