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Linear Combination Controls
Overview

The Linear Combinations controls are used to create and perform functions beyond the standard arithmetic functions in McIDAS-V. The Console tab consists of two parts - The Spectra and the Console:

Image 1: Linear Combination Controls Window

The Console allows a user to define multiple spectra and perform more complex mathematical operations.

Command line functions
• selector(wavenumber, color ) - Creates a spectra line with a optionally defined color and wavelength. If no wavenumber parameter is found, a data-dependent default value will be used. If no color parameter is found, the color of the selector bar will default to green. The spectra line can be dragged between wavelength/wavenumbers.
• Examples:
•  a = selector() [ Creates a green selector named "a" at a data-dependent wavenumber or wavelength] b = selector(1000) [ Creates a green selector named "b" at wavenumber 1000.0 ] c = selector('cyan') [ Creates a cyan selector named "c" at a data-dependent wavenumber or wavelength] d = selector(919.5, 'red') [ Creates a red selector named "d" at wavenumber 919.5 ] e = selector('40', 'orange') [ Creates a orange selector named "e" at the wavenumber? associated with band 40 ] f = selector('11') [ Creates a green selector named "f" at the wavenumber associated with band 11 ]
• combine(combination, name ) - Computes the mathematical operation corresponding to the expression entered. The results are available in the Field Selector under the "MultiSpectral" tree in the Fields tab listed under the optional name. If no name was specified, the results will be displayed using the expression that was computed. A combination is required for this function.
• Examples:
•  a = selector('2', 'red') [ Creates a red selector named "a" at the wavenumber associated with band 2] b = selector('1', 'yellow') [ Creates a yellow selector named "b" at the wavenumber associated with band 1] c = ((a-b)/(a+b)) [ Creates a variable c that corresponds to the expression ((a-b)/(a+b))] combine(c, 'NDVI') [ Results of the "c" variable will appear in the Field Selector as the "NDVI" entry ] combine((a-b)/(a+b)) [ Results of the expression in the combination field will appear in the Field Selector ]
• print( ) - Prints out information about the current wavelength/wavenumber of a selector, or its value.
Linear Combination Properties
• Spectra Window - Use the Shift+left click+drag combination to create a box of a region to zoom in on. To re-set the zoom level and return to the full spectra, use Ctrl+left click. Middle-clicking on a point in the spectra will change the wavenumber of the image displayed. Right click+drag will move the spectra left or right. Left click+drag on the wavelength/wavenumber selector bar(s) will allow you to change the wavelength

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