This function returns a reference to an ENVIConfusionMatrix object computed from a classification raster and truth regions of interest (ROIs).

The classification raster contains predicted class values from a classification, which are accompanied by class names. The truth ROIs contain the actual, or expected, class names of a particular region of the raster. A confusion matrix is created by comparing the predicted names to the truth names.

Example


The code example below evaluates classifications using a confusion matrix.

PRO EvaluateClassificationUsingConfusionMatrix
    COMPILE_OPT IDL2
 
    ; 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)
    File2 = Filepath('qb_boulder_roi.xml', Subdir=['data'], $
    Root_Dir=e.Root_Dir)
    Rois = envi.OpenROI(roiFile)
 
    ; Get training statistics
    StatTask = ENVITask('ROIStatistics')
    StatTask.INPUT_RASTER = Raster
    StatTask.INPUT_ROI = Rois
    StatTask.Execute
 
    ; Get the task from the catalog of ENVITasks
    Task = ENVITask('MahalanobisDistanceClassification')
 
    ; Define inputs
    Task.INPUT_RASTER = Raster
    Task.COVARIANCE = StatTask.Covariance
    Task.MEAN = StatTask.Mean
    Task.CLASS_PIXEL_COUNT = StatTask.Roi_Pixel_Count
    Task.CLASS_NAMES = [Rois[0].name, Rois[1].name, Rois[2].name]
    Task.CLASS_COLORS = [[0,0,255], [0,255,0], [255,0,0]]
 
    ; Run the task and display the result
    Task.Execute
    ClassRaster = Task.OUTPUT_RASTER
    View = e.GetView()
    Layer = View.CreateLayer(ClassRaster)
 
    ; Add the output to the Data Manager
    envi.Data.Add, ClassRaster
 
    ; Calculate the confusion matrix
    ConfusionMatrix = ENVICalculateConfusionMatrixFromRaster(ClassRaster, Rois)
 
    ; Print results
    Print, 'Confusion Matrix:'
    Print, ConfusionMatrix.Confusion_Matrix
    Print, 'Errors of commission: '
    Print, Transpose([[ConfusionMatrix.Column_Names+': '], [(ConfusionMatrix.CommissionError()).ToString()]])
    Print, 'Errors of omission: '
    Print, Transpose([[ConfusionMatrix.Column_Names+': '], [(ConfusionMatrix.OmissionError()).ToString()]])
    Print, 'Overall accuracy: ', ConfusionMatrix.Accuracy()
END

Syntax


Result = ENVICalculateConfusionMatrixFromRaster(Input_Raster, Input_ROIs [, Keywords=value])

Return Value


This function returns a reference to an ENVIConfusionMatrix object.

Arguments


Input_Raster

Specify a classification ENVIRaster.

Input_ROIs

Specify an array of ENVIROIs containing ground truth data.

Keywords


ERROR (optional)

Set this keyword to a named variable that will contain any error message issued during execution of this routine. If no error occurs, the ERROR variable will be set to a null string (''). If an error occurs and the routine is a function, then the function result will be undefined.

When this keyword is not set and an error occurs, ENVI returns to the caller and execution halts. In this case, the error message is contained within !ERROR_STATE and can be caught using IDL's CATCH routine. See IDL Help for more information on !ERROR_STATE and CATCH.

See Manage Errors for more information on error handling in ENVI programming.

Version History


ENVI 5.4

Introduced

API Version


4.3

See Also


ENVIConfusionMatrix, CalculateConfusionMatrixFromRaster Task