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ENVI_ICA_DOIT

ENVI_ICA_DOIT

Use the Independent Component Analysis (ICA) procedure to transform a set of mixed, random signals into components that are mutually independent.

This procedure has been replaced by the ENVIForwardICATransformTask.

Syntax


ENVI_DOIT, 'ENVI_ICA_DOIT' [, COEFF=variable], DIMS=array, FID=file ID [, FUNC_INDEX={0 | 1 | 2}] [, /IN_MEMORY] [, ITERATIONS=integer] [, M_FID=file ID] [, M_POS=value] [, MASK_VAL=value] [, OUT_BNAME=string array], OUT_NAME=string [, OUT_NB=long integer] [, OUT_TRANS_NAME=string], POS=array [, R_FID=variable] [, SAMPLE_DIMS=array] [, SAMPLE_XFAC=floating point] [, SAMPLE_YFAC=floating point] [, /SORT_OUTPUT}] [, STABILIZE_ITERATIONS=integer] [, THRESH=value]

Keywords


COEFF (optional)

Use this keyword when using LogCosh as the contrast function. Specify a coefficient value between 1.0 and 2.0. The default is 1.0.

DIMS

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

FID

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).

FUNC_INDEX (optional)

Use this keyword to specify the contrast function to use. Choose one of the following:

  • 0: LogCosh (default)
  • 1: Kurtosis
  • 2: Gaussian

LogCosh is a good general-purpose contrast function.

IN_MEMORY (optional)

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).

ITERATIONS (optional)

Use this keyword to specify the maximization iterations for IC optimization using a fixed-point algorithm. The default value is 100. More iterations helps ENVI Classic find more optimal components; however, each iteration adds to processing time, depending on the CPU and system load.

M_FID (optional)

Use this keyword to specify the file ID of the mask file. This value is returned from the keyword R_FID in the ENVI_OPEN_FILE procedure. M_FID is a long integer with a value greater than 0. An invalid file ID has a value of -1.

M_POS (optional)

Use this keyword to specify the band position of the mask band. M_POS is a long integer with a value greater than or equal to 0.

MASK_VAL (optional)

Use this keyword to specify the value for the masked pixels output. This keyword is valid only when you specify the M_FID and M_POS keywords. The default is 0.0.

OUT_BNAME (optional)

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

OUT_NAME

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.

OUT_NB (optional)

Use this keyword to specify the number of output IC bands. The default value is the number of input bands. For anomaly detection where the feature of interest occupies only a small portion of all pixels, it is not recommended to reduce the dimension of the data, as the anomaly will be buried in the noisy bands of PCA during data whitening.

OUT_TRANS_NAME (optional)

Use this keyword to specify the output transform filename and path. You can use this file in future IC calculations on the same image, or on an image with similar features.

POS

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:

  pos=[0,1,2,3]
              
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]
              
pos=[2,1,5,3]
              
envi_doit, 'cf_doit', dims=dims, fid=fid_array
              
out_name='test_composite_file'

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.

SAMPLE_DIMS (optional)

Use this five-element array of long integers that defines the spatial subset to define IC sample data. The default is the value set for the DIMS keyword. Defining a sample spatial subset smaller than the whole image can fit the IC sample into memory and increase computation speed, and helps concentrate the IC analysis on the features of interest in the spatial subset or ROI.

SAMPLE_XFAC (optional)

Use this keyword to specify the x resize factor for the IC sample data. The default is 1 (does not change the data). A value less than 1 causes the size to decrease. For example, using a resize factor of 0.5 will use every other pixel in the IC sample. Beware that setting this value to a small number could lose features of interest, as those pixels may be discarded.

SAMPLE_YFAC (optional)

Use this keyword to specify the y resize factor for the IC sample data. The default is 1 (does not change the data). A value less than 1 causes the size to decrease. For example, using a resize factor of 0.5 will use every other pixel in the IC sample. Beware that setting this value to a small number could lose features of interest, as those pixels may be discarded.

SORT_OUTPUT (optional)

If the keyword is set, ENVI Classic sorts output IC bands by decreasing spatial coherence. Use this option if a noisy band could appear as the first IC.

STABILIZE_ITERATIONS (optional)

Use this keyword to specify the maximization iterations for IC optimization using a stabilized fixed-point algorithm. When estimating one independent component, the fixed-point algorithm runs first. If the algorithm does not converge after maximization iterations, then the stabilized fixed-point algorithm runs to improve convergence. The default is 100. Enabling stabilization and increasing stabilization iterations helps ENVI Classic find the optimal components; however, each iteration adds to processing time, depending on the CPU and system load.

THRESH (optional)

Use this keyword to specify a floating-point or double-precision minimum change threshold for IC optimization. Specify a value from 0 to 1. The default is 0.0001. The allowable range is 10-8 to 10-2. Increasing this value increases the speed of convergence, but may provide a less optimal solution.



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