About virtual variables

A virtual variable is created by applying an operator (a mathematical algorithm) to one or more input acoustic variables (operands). Operands may be raw variables or other virtual variables.

Operators may be chained to create additional virtual variables; that is, by using the output of one virtual variable as input to another (see example below).

When using a long chain of virtual variables, the calculations may take a significant amount of time. A progress bar is provided to indicate how quickly the calculation is proceeding. To stop the calculation, press and hold ESC while this progress bar is displayed.

You view and manage virtual variables using the Dataflow window .

To create a virtual variable:

Display the Dataflow window
On the Object menu, point to New then click Variable
On the New variable dialog box, choose the desired operator

Notes:

All virtual variables take a copy of their variable properties from their first operand, see Inheritance of Properties for more information.
The Calibration settings and Transducer for complex virtual chains of pre-Echoview 5 EV files may change to conform with the Echoview 5 rule for the inheritance of properties from the first operand. Refer to Inheritance of Properties for more information.
Most virtual variables take unprocessed data from their operands. See About setting variable properties for more information.
If a virtual variable requires multiple operands, Echoview will only process pings that have compatible ping geometry in all operands, see Using multiple operands for more information.
You can only export data from virtual echograms if you have purchased the Virtual Echograms module license, see Virtual echogram license restrictions.
Virtual variables are unavailable if any of their operands is not able to provide data (i.e. are also unavailable)

Example:

Shown below, is the creation of a "dB differences" virtual variable using various operators and operands.

dB difference

A description of virtual echograms is provided in the following publication:

Higginbottom, I.R., Pauly, T.J. and Heatley D.C. (2000). Virtual echograms for visualization and post-processing of multiple-frequency echosounder data. Proceedings of the Fifth European Conference on Underwater Acoustics, ECUA 2000 (Ed. M.E. Zakharia), 1497-1502.

About virtual variables

See also