ChangeThresholdClassification Task

This task lets you manually set the threshold needed to classify change detection between two images.

Example

This example performs a difference analysis between two images from different dates, then it sets thresholding values for change detection. The images represent NCEP-Reanalysis 2 air temperatures (K) at the 1000-isobar level, at 0600 hours Zulu time. The first image is from 29 December 2012, and the second is from 31 December 2012. Each image has one band. This example uses sample data from the ENVI installation path.

; Start the application

e = ENVI()

TimeSeriesDir = Filepath('', Subdir=['data','time_series'], $

  Root_Dir = e.Root_Dir)

files = File_Search(TimeSeriesDir, 'AirTemp*.dat')

numRasters = N_Elements(files)

rasters = ObjArr(numRasters)

FOR i=0, (numRasters-1) DO $

  rasters[i] = e.OpenRaster(files[i])

; Get the task from the catalog of ENVITasks

Task = ENVITask('BuildTimeSeries')

; Define inputs

Task.INPUT_RASTERS = rasters

; Run the task

Task.Execute

; Get the raster that corresponds to 0600,

; 29 December 2012 (index #1).

; Indices are zero-based.

SeriesFile = Task.OUTPUT_RASTERSERIES

SeriesFile.Set, 0

Image1 = SeriesFile.Raster

; Get the raster that corresponds to 0600,

; 31 December 2012 (index #9).

; Indices are zero-based.

SeriesFile.Set, 8

Image2 = SeriesFile.Raster

; Get the task from the catalog of ENVITasks

Task = ENVITask('ImageBandDifference')

; Define inputs

Task.INPUT_RASTER1 = Image1

Task.INPUT_RASTER2 = Image2

; Define outputs

Task.OUTPUT_RASTER_URI = e.GetTemporaryFilename()

; Run the task

Task.Execute

; Get the task from the catalog of ENVITasks

ChangeThresholdTask = ENVITask('ChangeThresholdClassification')

; Define inputs

ChangeThresholdTask.INPUT_RASTER = Task.OUTPUT_RASTER

; Define increase and/or decrease values

ChangeThresholdTask.INCREASE_THRESHOLD = 0.0377000

ChangeThresholdTask.DECREASE_THRESHOLD = 0.411400

; Run the task

ChangeThresholdTask.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, ChangeThresholdTask.OUTPUT_RASTER

; Display the result

View = e.GetView()

Layer = View.CreateLayer(ChangeThresholdTask.OUTPUT_RASTER)

Syntax

Result = ENVITask('ChangeThresholdClassification')

Input properties (Set, Get): DECREASE_THRESHOLD, INCREASE_THRESHOLD, INPUT_RASTER, OUTPUT_RASTER_URI

Output properties (Get only): OUTPUT_RASTER

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

Methods

This task inherits the following methods from ENVITask:

Properties

This task inherits the following properties from ENVITask:

COMMUTE_ON_DOWNSAMPLE

DECREASE_THRESHOLD (optional)

Specify the decrease threshold to show areas of decrease.

INCREASE_THRESHOLD (optional)

Specify the increase threshold to show areas of increase.

INPUT_RASTER (required)

Specify a raster on which to threshold.

OUTPUT_RASTER

This is a reference to the output raster of filetype ENVI.

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 property, or set it to an exclamation symbol (!), a temporary file will be created.

Version History

ENVI 5.2

Introduced

API Version

4.3