ISODATAClassification Task

This task clusters pixels in a dataset based on statistics only, without requiring you to define training classes. It uses the ISODATA unsupervised method for classification.

The ISODATA method starts by calculating class means evenly distributed in the data space, then iteratively clusters the remaining pixels using minimum distance techniques. Each iteration recalculates means and reclassifies pixels with respect to the new means. This process continues until the percentage of pixels that change classes during an iteration is less than the change threshold or the maximum number of iterations is reached.

Example

; Start the application

e = ENVI()

; Open an input file

File = Filepath('qb_boulder_msi', Subdir=['data'], $
  Root_Dir=e.Root_Dir)

Raster = e.OpenRaster(File)

; Get the  task from the catalog of ENVITasks

Task = ENVITask('ISODATAClassification')

; Define inputs

Task.INPUT_RASTER = Raster

; Run the task

Task.Execute

; Get the collection of data objects currently available in the Data Manager

DataColl = e.Data

; Add the output to the Data Manager

DataColl.Add, Task.OUTPUT_RASTER

; Display the result

View = e.GetView()

Layer = View.CreateLayer(Task.OUTPUT_RASTER)

Syntax

Result = ENVITask('ISODATAClassification')

Input parameters (Set, Get): INPUT_RASTER, CHANGE_THRESHOLD_PERCENT, ITERATIONS, NUMBER_OF_CLASSES, OUTPUT_RASTER_URI

Output parameters (Get only): OUTPUT_RASTER

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

CHANGE_THRESHOLD_PERCENT (optional)

The change threshold percentage that determines when to complete the classification. When the percentage of pixels that change classes during an iteration is less than the threshold value, the classification completes. The default value is 2.0.

INPUT_RASTER (required)

Specify a raster on which to perform unsupervised classification.

ITERATIONS (optional)

The maximum iterations to perform. If the change threshold percent is not met before the maximum number of iterations is reached, the classification completes. The default value is 10.

NUMBER_OF_CLASSES (optional)

Specify the number of classes to generate. The default value is 5.

OUTPUT_RASTER_URI (optional)

Specify a string with the fully qualified filename and path of the associated OUTPUT_RASTER.

If you do not specify this parameter, or set it to an exclamation symbol (!), ENVI creates a temporary file.
If you set it to the hash symbol (#), ENVI creates a file in the temporary directory, but this file will not be deleted when ENVI closes.