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
e = ENVI()
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)
StatTask = ENVITask('ROIStatistics')
StatTask.INPUT_RASTER = Raster
StatTask.INPUT_ROI = Rois
StatTask.Execute
Task = ENVITask('MahalanobisDistanceClassification')
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]]
Task.Execute
ClassRaster = Task.OUTPUT_RASTER
View = e.GetView()
Layer = View.CreateLayer(ClassRaster)
envi.Data.Add, ClassRaster
ConfusionMatrix = ENVICalculateConfusionMatrixFromRaster(ClassRaster, Rois)
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
API Version
4.3
See Also
ENVIConfusionMatrix, CalculateConfusionMatrixFromRaster Task