Sidescan Mosaics

Sidescan mosaics allow a number of sonar track logs to be combined into a single, large image.

A Sidescan Mosaic made up of around 20 individual sonar logs

·The process of creating a sidescan mosaic involves selecting regions of sidescan from one or more tracks, adding these to the mosaic and then configuring the individual segments to produce a finished mosaic.

·Once a mosaic has been produced, it can be exported in one of the available image formats, before being used as a map layer within an Map Projects, a background image or in further GIS applications such as Google Earth.

Creating a new Sidescan Mosaic

The Sidescan Mosaic asset type appears between Waypoints and Images in the Asset Library, and is only visible if the sidescan mosaic module has been purchased and activated:

New sidescan mosaics can be created using the File/New/Sidescan Mosaic menu option, and opened for editing by double-clicking the mosaic name in the list, in the same way as any other ReefMaster asset (see the Asset Library for more details).

A new mosaic can also be created whilst adding tracks or track parts - see below.

Sidescan Segments

Sidescan mosaics are simply a collection of one or more tracks (or parts of tracks) that contain sidescan sonar information. Each track (or track part) that is added to a sidescan mosaic is known as a sidescan segment, and each segment can be edited independently for properties such as port and starboard ranges, brightness, contrast, opacity and z-order (the drawing order of the segment relative to other segments).

Adding Tracks and Track Parts to a Sidescan Mosaic

Creating a sidescan mosaic involves choosing regions of sidescan to combine together to produce a finished image.

Adding whole tracks to a sidescan mosaic

To add a whole track to a sidescan mosaic, right-click the required track in the Asset Library and select the menu option Add Track to Mosaic (multiple tracks can be added to a mosaic by selecting the required tracks in the asset library track list, before activating the right-click menu). Choose either the New Mosaic option, which creates a new sidescan mosaic, or select an existing sidescan mosaic from the list provided:

Alternatively, tracks (or groups of tracks) can be added to an open Sidescan Mosaic edit window by dragging from the asset library with the left mouse button held down.

Adding parts of a track to a sidescan mosaic

It can make the subsequent editing of sidescan mosaics easier if the useful areas of sidescan data are selected before they are added to the mosaic.

To add just a part of track to a sidescan mosaic, open the required track for editing and place the track edit window into sidescan mode. Examine the sidescan swath to locate a region of interest, right-click the swath edge and choose the Add to Mosaic menu option. The selected range will be added to the chosen mosaic:

Adding a segment range to a mosaic from the track edit window

Note that:

·Only the sidescan data within the specified start/end times is added to the mosaic.

·All other settings, including port and starboard ranges, brightness, contrast etc. will be copied with the segment, but can still be edited within the mosaic. This includes increasing the port or starboard ranges.

·Any number of ranges can be added to a mosaic from a track, including ranges that overlap in time.

Editing Sidescan Mosaics

Editing sidescan mosaics consists of adding sidescan swaths to a Sidescan Mosaic and editing individual swath segments to produce a finished mosaic, which can then be exported as an image file.

The sidescan mosaic edit window contains a graphical editing area where all of the component segments are displayed.

When a sidescan mosaic is the being edited, the Sidescan menu bar is displayed Edit panel contains the editable properties of the sidescan mosaic.

1, 3.Mosaic Properties

Mosaic properties include the palette, display mode, noise reduction, sharpening, auto-gain and brightness and contrast.

2. Selected Segment Properties

Segment controls include brightness, constrast, opacity and port and starboard ranges. These controls are also available in the right-button menu for segments,

4. Segment List

Every segment within the mosaic is shown as a row in the Segment List, where they can be selected, deleted or moved within the Z-order.

Mosaic Properties

Mosaic properties include the mosaic name, brightness, contrast, palette and auto-gain, noise-reduction and sharpening, which apply to all segments within the mosaic.

Brightness, contrast and opacity can also be adjusted on a per-segment basis. The displayed brightness and contrast of a given segment is a combination of both mosaic and segment settings.

Mosaic properties are available in the Sidescan Mosaic edit panel and replicated the Sidescan Menu:

1. Mosaic Name

2. Signal Display

The signal display affects which sonar return signal is displayed when sidescan swathes overlap.

In the track display, signal display can be on of:

Layered

Segments are drawn according to the order specified in the Segments List, and can be moved up or down in the Z-order by dragging within the list or using the up and down buttons.

Closest Signal

The signal closest to the transducer is shown in preference to signals from further away. This mode usually results in the best available signal being shown when swaths overlap, without having to perform any editing of port or starboard ranges for overlapping segments.

Blend Closest

Similar to Closest Signal, but with additional blending at points of swath overlap. This mode gives the very best results for overlapping mosaics. Note that when using Blend Closest mode, segments within the map view do not change their appearance when selected.

3. Noise reduction

Noise reduction can help in reducing the effects of interference on the sonar image. To enable noise reduction, check the Noise Reduction check-box. Noise reduction is available in two versions; x1 and x2, where x1 provides basic noise reduction suitable for most sonar recordings, and x2 provides a more aggressive form of noise reduction that may be useful for particularly noisy sonar logs. Note that the x2 noise reduction variant may result in some loss of image detail.

5. Sharpening

The sharpening tool uses hardware accelerated image process techniques to increase image sharpness and local contrast. The degree of sharpening applied can be varied by used the slider.

5. Autogain

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. The impact of auto-gain can be adjusted from 0 (none) to 1 (full) by using the slider.

6. Brightness

7. Contrast

8. Palette selector

The selected palette always apply to the whole mosaic.

Editing segments

Individual segments can be edited via the Sidescan Menu, the swath control bar and the right-click menu, which can be activated by holding the mouse pointer over a segment edge in the graphical edit area, or a segment row in the segment list, and clicking the right mouse button.

The Swath Control Bar

The swath control bar is shown at the bottom of the graphical edit area, and controls the start and end points of currently selected segment.

Segment Settings

Segment editing operations are carried out in the Selected Segment section of the Sidescan Menu or via the segment menu, which is activated using the right mouse button whilst holding the mouse pointer over a segment in either the graphical edit area or the segment list:

1, 2. Opacity, brightness, contrast and port and starboard ranges

Port and starboard range, brightness, contrast and opacity work in the same way as they do in the Sidescan Mosaic Track Review, where they are described in detail.

3. Split segment

A segment is the smallest editable unit of a sidescan mosaic. To apply different settings, such as contrast or brightness, to different parts of a swath, or to entirely remove sections of a swath, an existing segment can be split. Splitting a segment cuts the segment at the start and end times set within the swath control bar, which results in a total of up to three segments; the existing visible range becomes one segment, any part prior to the start position of the existing range becomes another, and any part after the end position of the current range becomes another. Each of these segments can then be independently edited.

4. Delete segment

Remove the segment from the mosaic. This operation can be undone.