ResampleSpectrum Task

This task resamples a given spectrum to a different set of wavelengths, typically from a hyperspectral image.

Example

; Launch the application

e = ENVI()

; Open a spectral library

specLibFile = FILEPATH('veg_2grn.sli', ROOT_DIR=e.ROOT_DIR, $

  SUBDIR=['resource', 'speclib', 'veg_lib'])

specLib = ENVISpectralLibrary(specLibFile)

; Open a hyperspectral image

file = FILEPATH('AVIRISReflectanceSubset.dat', $

  ROOT_DIR=e.ROOT_DIR, $

  SUBDIRECTORY = ['data', 'hyperspectral'])

raster = e.OpenRaster(file)

; Get wavelength units of raster

Task1 = ENVITask('RasterMetadataItem')

Task1.INPUT_RASTER = raster

Task1.KEY = 'Wavelength Units'

Task1.Execute

; Get wavelengths of raster

Task2 = ENVITask('RasterMetadataItem')

Task2.INPUT_RASTER = raster

Task2.KEY = 'Wavelength'

Task2.Execute

; Get the selected spectrum from spectral library

Task3 = ENVITask('GetSpectrumFromLibrary')

Task3.INPUT_SPECTRAL_LIBRARY = specLib

Task3.SPECTRUM_NAME = 'Dry Grass'

Task3.Execute

; Plot the spectrum

y3 = Task3.SPECTRUM

x3 = Task3.WAVELENGTHS

origPlot = PLOT(x3,y3, 'r2', $

  TITLE='Dry Grass (original)', $

  XTITLE='Wavelengths (um)', $
  YTITLE='Data Value')

; Get the resample spectrum task from the catalog of ENVITasks

Task4 = ENVITask('ResampleSpectrum')

; Define inputs

; Spectrum from library to be resampled

Task4.INPUT_SPECTRUM = Task3.SPECTRUM

; Wavelengths from spectral library

Task4.INPUT_WAVELENGTHS = Task3.WAVELENGTHS

; Wavelength units from spectral library

Task4.INPUT_WAVELENGTH_UNITS = Task3.WAVELENGTH_UNITS

; Wavelengths from raster

Task4.RESAMPLE_WAVELENGTHS = Task2.VALUE.VALUE

; Wavelength units from raster

Task4.RESAMPLE_WAVELENGTH_UNITS = Task1.VALUE.VALUE

; Run the resample spectrum task

Task4.Execute

; Plot the resampled spectrum

y4 = Task4.OUTPUT_SPECTRUM

x4 = Task3.WAVELENGTHS

specLibPlot = PLOT(x4,y4, 'g2', $

  TITLE='Dry grass (resampled)', $

  XTITLE='Wavelengths (um)', $
  YTITLE='Data Value')

Syntax

Result = ENVITask('ResampleSpectrum')

Input parameters (Set, Get): INPUT_SPECTRUM, INPUT_WAVELENGTHS, INPUT_WAVELENGTH_UNITS, MISSING, RESAMPLE_WAVELENGTHS, RESAMPLE_WAVELENGTH_UNITS

Output parameters (Get only): OUTPUT_SPECTRUM

Parameters marked as "Set" are those that you can set to specific values. You can also retrieve their current values any time. Parameters marked as "Get" are those whose values you can retrieve but not set.

Input Parameters

INPUT_SPECTRUM (required)

Specify an array that represents the spectrum to resample.

INPUT_WAVELENGTHS (required)

Specify an array that represents the wavelength values for a given spectrum.

INPUT_WAVELENGTH_UNITS (optional)

The units of the input wavelengths.

MISSING (optional)

Specify the value to use for a spectra that falls outside the input wavelength range. The default value is 0.

RESAMPLE_WAVELENGTHS (required)

Specify an array that represents the wavelengths to resample the input spectrum to. This can come from an image (using the RasterMetadataItem task) or from your own array of values.