This routine has been replaced by the ENVIROI::AddThreshold method.

Use this procedure to create an ROI that contains all pixels with values above, below, or between threshold pixel values.

Syntax

ENVI_DOIT, 'ROI_THRESH_DOIT', DIMS=array, FID=file ID, MAX_THRESH=value, MIN_THRESH=value, /NO_QUERY, POS=array, ROI_ID=variable, ROI_NAME=string, ROI_COLOR=long integer

Keywords

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).

MAX_THRESH

Use this keyword to specify the maximum threshold. Values below MAX_THRESH are included in the ROI.

MIN_THRESH

Use this keyword to specify the minimum threshold. Values above MIN_THRESH are included in the ROI.

NO_QUERY

Set this keyword to suppress informational or interactive dialogs during the threshold process.

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'

ROI_COLOR

Use this keyword to specify the output ROI color. ROI_COLOR is a long-integer variable representing the index into the ENVI Classic graphic colors. By default, ENVI Classic has 17 graphic colors, whose index values range from 0 to 16.

ROI_ID

Set this keyword to a named variable containing the ID of the resulting ROI.

ROI_NAME

Use this keyword to specify an output name for the ROI.