This routine is obsolete and has been replaced by the ResampleSpectrum task.

This procedure spectrally resamples image or spectral library files. Resampled spectral libraries are added to the Available Bands List.


ENVI_DOIT, 'ENVI_SPECTRAL_RESAMPLING_DOIT' [, BAD_VALUE=value] [, /COMPRESSION], DIMS, FID=file ID, /IN_MEMORY [, OUT_BNAME=string array] [, OUT_DT=integer] [, OUT_FWHM=array], OUT_NAME=string, OUT_WAVELENGTH_UNITS=integer, OUT_WL=array, POS=array [, R_FID=file ID]


BAD_VALUE (optional)

Use this keyword to specify a value to use for spectra that fall outside the input wavelength range. In this case, no extrapolation will be performed. All spectra values equal to BAD_VALUE are considered bad values. BAD_VALUE is a single number.

COMPRESSION (optional)

Set this keyword to write the file using the standard GZIP format. IDL’s GZIP support is based on the freely available ZLIB library by Mark Adler and Jean-loup Gailly (see http:\\ for details). This means that IDL’s compressed files are 100% compatible with the widely available gzip and gunzip programs.


The “dimensions” keyword is a five-element array of long integers that defines the spatial subset (of a file or array) to use for processing. Nearly every time you specify the keyword FID, you must also specify the spatial subset of the corresponding file (even if the entire file, with no spatial subsetting, is to be processed).

  • DIMS[0]: A pointer to an open ROI; use only in cases where ROIs define the spatial subset. Otherwise, set to -1L.
  • DIMS[1]: The starting sample number. The first x pixel is 0.
  • DIMS[2]: The ending sample number
  • DIMS[3]: The starting line number. The first y pixel is 0.
  • DIMS[4]: The ending line number

To process an entire file (with no spatial subsetting), define DIMS as shown in the following code example. This example assumes you have already opened a file using ENVI_SELECT or ENVI_PICKFILE:

  envi_file_query, fid, dims=dims


The file ID (FID) is a long-integer scalar with a value greater than 0. An invalid FID has a value of -1. The FID is provided as a named variable by any routine used to open or select a file. Often, the FID is returned from the keyword R_FID in the ENVIRasterToFID routine. Files are processed by referring to their FIDs. If you work directly with the file in IDL, the FID is not equivalent to a logical unit number (LUN).


Set this keyword to specify that output should be stored in memory. If you do not set IN_MEMORY, output will be stored on disk and you must specify OUT_NAME (see below).

OUT_BNAME (optional)

Use this keyword to specify a string array of output band names.

OUT_DT (optional)

This keyword indicates the IDL data type of the output data. Set the keyword to one of the following integer values.

Note: For spectral libraries, the output data type is always floating-point.

  • 1: Byte (8 bits)
  • 2: Integer (16 bits)
  • 3: Long integer (32 bits)
  • 4: Floating-point (32 bits)
  • 5: Double-precision floating-point (64 bits)
  • 6: Complex (2x32 bits)
  • 9: Double-precision complex (2x64 bits)
  • 12: Unsigned integer (16 bits)
  • 13: Unsigned long integer (32 bits)
  • 14: Long 64-bit integer
  • 15: Unsigned long 64-bit integer

The default output type is the data type of the input file.

OUT_FWHM (optional)

Use this keyword to specify a floating-point array of FWHM responses for each output band. The number of elements in this array is equal to the number of output bands.


Use this keyword to specify a string with the output filename for the resulting data. If you set the keyword IN_MEMORY, you do not need to specify OUT_NAME.


Use this keyword to specify an integer value representing the units used for the values of the OUT_WL array.

  • 0: Micrometers
  • 1: Nanometers
  • 2: Wavenumber
  • 3: GHz
  • 4: MHz
  • 5: Index
  • 6: Unknown


Use this keyword to specify an array of wavelengths to resample to.


Use this keyword to specify an array of band positions, indicating the band numbers on which to perform the operation. This keyword indicates the spectral subset of bands to use in processing. POS is an array of long integers, ranging from 0 to the number of bands minus 1. Specify bands starting with zero (Band 1=0, Band 2=1, etc.) For example, to process only Bands 3 and 4 of a multi-band file, POS=[2, 3].

POS is typically used with individual files. The example code below illustrates the use of POS for a single file with four bands of data:

envi_doit, 'envi_stats_doit', dims=dims, fid=fid, pos=pos, $
comp_flag=3, dmin=dmin, dmax=dmax, mean=mean, stdv=stdv, hist=hist

But what if you need to create an output file consisting of data from different bands, each from different files? Library routines such as CF_DOIT and ENVI_LAYER_STACKING_DOIT can accomplish this, but they use the POS keyword differently. Suppose you have four files, test1, test2, test3, and test4, with corresponding FIDs of fid1, fid2, fid3, and fid4, respectively. In the following example, you want Band 3 from test1 in the first position, Band 2 from test2 in the second position, Band 6 from test3 in the third position, and Band 4 from test4 in the fourth position. The code should be as follows:

  fid_array = [fid1,fid2,fid3,fid4]
envi_doit, 'cf_doit', dims=dims, fid=fid_array

R_FID (optional)

ENVI Classic library routines that result in new images also have an R_FID, or “returned FID.” This is simply a named variable containing the file ID to access the processed data. Specifying this keyword saves you the step of opening the new file from disk.