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ENVI

ENVIPixelwiseBandMathRaster

ENVIPixelwiseBandMathRaster

This function constructs an ENVIRaster from a source raster that has a simple mathematical expression applied on a pixel-by-pixel basis.

The result is a virtual raster, which has some additional considerations with regard to methods and properties. See Virtual Rasters for more information.

Example


This example calculates an Enhanced Normalized Difference Vegetation Index (ENDVI, source: MaxMax.com).

; Start the application
e = ENVI()
 
; Open an input file
file = FILEPATH('qb_boulder_msi', ROOT_DIR=e.ROOT_DIR, $
  SUBDIRECTORY = ['data'])
raster = e.OpenRaster(file)
 
; Calculate enhanced NDVI
expression = '((b4 + b2) - 2*b1) / ((b4 + b2) + 2*b1)'
bandMathRaster = ENVIPixelwiseBandMathRaster(raster, expression)
 
; Display the result
View = e.GetView()
Layer = View.CreateLayer(bandMathRaster)

Syntax


Result = ENVIPixelwiseBandMathRaster(Input_Raster, Expression, ERROR=variable)

Return Value


This routine returns a reference to an ENVIRaster.

Arguments


Input_Raster

Specify the input ENVIRaster.

Expression

Enter a string indicating the mathematical expression.

  • The currently supported operators include +, -, *, and /. More operators will be added in a future release.
  • Name the band variables as bx, where x is the order of the band in the raster. For example, b1 is the first band in the raster, b2 is the second band, etc.

Methods


This virtual raster inherits methods and properties from ENVIRaster; however the following methods will override the ENVIRaster methods:

Dehydrate

Hydrate

Keywords


ERROR (optional)

Set this keyword to a named variable that will contain any error message issued during execution of this routine. If no error occurs, the ERROR variable will be set to a null string (''). If an error occurs and the routine is a function, then the function result will be undefined.

When this keyword is not set and an error occurs, ENVI returns to the caller and execution halts. In this case, the error message is contained within !ERROR_STATE and can be caught using IDL's CATCH routine. See IDL Help for more information on !ERROR_STATE and CATCH.

See Manage Errors for more information on error handling in ENVI programming.

Version History


ENVI 5.3, Service Pack 1

Introduced

ENVI 5.4

Added Dehydrate and Hydrate methods

See Also


ENVIRaster


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