Supervised classification (Tutorial)

Revision as of 21:20, 13 May 2018

Add the Sentinel-2 imagery Subset_S2A_MSIL2A_20170619T_MUL_BOA.tif into a QGIS project.
Calculate mean and standard error for each band of the Sentinel-2 imagery using the OTB Graphical User Interface.

In the Search box on the Windows Start menu type OSGeo4W Shell. You should be able to open the shell by clicking on it.
Type into the shell: otbgui_ComputeImagesStatistics.

Select a multiband input file and an output XML file as seen in the screenshot.

Add the training areas as vector polygon file lab05_training_input.shp into QGIS.
Open Orfeo Toolbox --> TrainImageClassifier (libsvm) to use the Support Vector Machine SVM algorithm (see figure B).
Set Subset_S2A_MSIL2A_20170619T_MUL_BOA.tif as Input image list.
Set lab05_training_input.shp as Input vector list.
Set Subset_S2A_MSIL2A_20170619T_MUL_BOA.tif.xml as Input XML image statistics file.
Set Name of discrimination field to C_ID (C_ID refers to the column that contains the LUC code).
Save the Output confusion matrix as ConfusionMatrixSVM.csv.
Save the Output model as SVM.model.
Calculation of accuracies :
Open ConfusionMatrixSVM.csv in LibreOffice or MS Excel and calculate overall, producer and consumer accuracies.

Open Orfeo Toolbox --> Image Classification (see figure C).
Set Subset_S2A_MSIL2A_20170619T_MUL_BOA.tif as Input image.
Set SVM.model as Model file.
Set Subset_S2A_MSIL2A_20170619T_MUL_BOA.xml as Statistical file.
Save the Output image as su_svm.tif.
Evaluate classification results.
1. Add the classification result su_svm.tif to QGIS.
2. Right click su_svm.tif in the TOC and select Properties --> Style --> Style --> Load Style.
3. Load lab05_MinDist.qml.

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-=== Figures ===
-{|class="wikitable" style="border:0pt"
-|style="border:0pt"|[[Image:ComputeImage.png|thumb|450px|'''Figure A''': Dialogues of the ''Compute images second order statistics'']]
-|style="border:0pt"|[[Image:TrainImageClassifier.png|thumb|450px|'''Figure B''': Dialogues of the ''TrainImageClassifier (libsvm)'']]
-|-
-|style="border:0pt"|[[Image:ImageClassification.png|thumb|450px|'''Figure C''': Dialogues of the ''Image Classification'']]
-|style="border:0pt"|[[Image:ComputeConfusionMatrix.png|thumb|450px|'''Figure D''': Dialogues of the ''ComputeConfusionMatrix (Vector)'']]
-|}
 [[Category:Image classification]]