.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 Variables and Geometry window .
Notes:
All virtual variables take a copy of their variable properties from their first operand, see Inheritance of Properties for more information.
You can choose to inherit virtual variable calibration settings from a donor variable. See Inheritance of calibration settings 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.
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 variables
Creating and deleting virtual variables
Data types
Operators
New variable dialog box
Variables and geometry window
Importing virtual variables
Inheritance of properties
Calibration settings for virtual variables