About Cruise Tracks

A cruise track is a graphic representation of the geographic position data in a position variable, optionally combined with the data in an acoustic variable. There are three types of cruise track in Echoview:

GPS fixes

GPS fixes cruise tracks are created from position variables and provide information on the status of the GPS data.

To display a GPS fixes cruise track, do one of the following:

On the View menu, point to Cruise Track , and then click a position variable.
Note: If you have created multiple filesets or virtual variables you will have to point to the fileset that contains the variable after pointing to Echogram.
On the Filesets window; double-click a position variable, or select a position variable and click Cruise Track .
On the Dataflow window; double-click a position variable icon, or right-click on a position variable icon then click Cruise Track

Cruise track window features

GPS fixes are displayed in the following way:

The first fix is displayed as a small black or gray square (top left in the example).
The last fix is displayed as a small black or gray circle (bottom right in the example).
Good GPS fixes are displayed as small green crosses.
Bad GPS fixes are displayed as small red crosses.

Notes

If the cruise track is synchronized with an echogram or table, the GPS fix selected on the echogram is shown by a black circle and crosshairs (towards the top left in the example). You can also double-click on a point on an echogram, or a row in a table, and view that point on the synchronized echogram.
When you move the mouse along the cruise track, the GPS fix closest to the mouse is tracked by a small blue circle (shown adjacent to the mouse in the example).
Good and Bad fixes are only displayed if selected on the Display page of the Variable Properties dialog box.

GPS fixes are joined by a continuous line to form the cruise track. The first, last, and all good fixes are used.

The color of each line segment shows the status of interpolated positions:

Green	indicates the position status	good
Magenta	indicates the position status	uncertain

Notes:

Cruise tracks are created from processed GPS fixes. You enter processing settings on the Data page of the Variable properties dialog box. See Processing and smoothing cruise tracks for more information..
To smooth a cruise track you must create a virtual position variable using the Kalman GPS smoothing filter operator. See Processing and smoothing cruise tracks for more information.
Cruise tracks plot the position of the GPS antenna, the position of the platform may be offset from the position of the GPS antenna as defined via the Platform Properties dialog box.
Position status is also shown on the position status bar on an echogram.
The coordinate system used on cruise track windows may be either latitude/longitude or eastings/northings. This is determined by the Map Projection selected on the Mapping page of the EV File Properties dialog box.

Along-track display

Along-track display is a color-coded cruise track showing integration or other processing results derived from an acoustic variable. For example, it is possible to create a cruise track showing the depth of the sea floor, or the mean Sv value, as seen below. Along-track displays can only be created from raw or virtual variables with a data type of Sv.

To display an Along-track display, do one of the following:

On the View menu, point to Cruise Track, and then click an acoustic variable.
Note: If you have created multiple filesets or virtual variables you will have to point to the fileset that contains the variable after pointing to Echogram.
On the Filesets window, select an acoustic variable and click Cruise Track .
On the Dataflow window, right-click on an acoustic variable icon then click Cruise Track.

Analysis results that can be output to an along-track display are:

Mean Sv
Minimum Sv
Maximum Sv
NASC (nautical area scattering co-efficient)
ABC (area backscattering co-efficient)
Area backscattering strength (10logABC)
Mean "exclude below" line depth
ping status

To select analysis results for output to an along-track display, see Using cruise tracks: Along track display.

Each segment on the cruise track shows the mean value of the selected analysis variable calculated across a range of pings. The range of pings for each segment is determined by the time/distance grid settings in the Variable Properties dialog box and can be based on time, distance, or number of pings. In the above example, each segment in the cruise track shows the mean Sv for every 20 pings of data.

Notes:

Calculation of results for along-track display is also affected by all Echoview settings that affect processing such as data thresholds, exclusion lines, and bad data regions. See About setting variable properties for a detailed description of how Echoview settings affect output.
The along-track display plots the position of the transducer that has been applied to the Sv variable on the Calibration page of the Variable Properties dialog box. If the transducer position varies from the GPS antenna position then the along-track display will vary from the cruise track of GPS positions.
An along-track display of ping status is not affected by the time/distance grid setting. The intervals displayed on the cruise track are the same as the intervals set on the echogram.
The coordinate system used on cruise track windows may be either latitude/longitude or eastings/northings. This is determined by the Map Projection selected on the Mapping page of the EV File Properties dialog box.

3D cruise tracks

3D cruise tracks are a 3D object which can be added to scenes.

The 3D cruise track plots the position of the GPS antenna. See About transducer geometry for further information about how the position of the GPS antenna is specified.

See Displaying a 3D cruise track and Using a 3D cruise track for scene animation for further information.

Cruise track scale bar

To display a scale bar for the cruise track window, select Show scale bar on the Display page of the Variable properties dialog box. The scale bar shows nautical miles (nmi) and kilometers/meters (km or m).

Note: This is not available on 3D cruise tracks.

What is plotted where?

To summarize what is plotted where, each of the three types of cruise track plots the course of a slightly different point in the echosounding system as follows:

	GPS fix cruise tracks		position of the GPS antenna
	along track display cruise tracks		position of the transducer
	3D cruise tracks		position of the GPS antenna

See About transducer geometry for more information on how these three positions interrelate.

Define a region

The Vertical band tool enables you to make a selection on a cruise track which extends the entire depth of the echogram at a defined time/GPS position. The selection is displayed as a region which follows the cruise track and starts at the nearest good GPS fix to the mouse pointer and ends at the nearest good GPS fix to the mouse pointer. To define the marker region, on the Shortcut menu select Define Region.

See Using cruise tracks - Define a region for more information.