From GIS to Remote SensingThis post is about a major update for the Semi-Automatic Classification Plugin for QGIS 2.0, version 2.4.0.
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| The Semi-Automatic Classification Plugin v. 2.4.0 |
Following the changelog:
-new button for the manual drawing of ROIs
-new ID field for macroclass, which allow for the definition of a macroclass (a group of ROIs having different class ID)
-new classification option (Use Macroclass ID), which allows the land cover classification using the macroclass field
-new tab for the scatter plots of ROIs
-code improvements
-new ID field for macroclass, which allow for the definition of a macroclass (a group of ROIs having different class ID)
-new classification option (Use Macroclass ID), which allows the land cover classification using the macroclass field
-new tab for the scatter plots of ROIs
-code improvements
This update brings several improvements. First, a button in the ROI creation dock allows for the manual drawing of ROIs, which can be useful to define heterogeneous surfaces. After clicking the button, left click on the image to define the ROI vertices; right click on the image to define the last vertex and close the polygon.
A new ID field allows for the definition of a macroclass for each ROI. A macroclass is a group of ROIs having different Class ID.
This is related to the option Use Macroclass ID. If checked, it allows for the land cover classification using the macroclass field. The macroclass is useful when we need to classify materials that have different spectral signatures, but we want in the same land cover class (i.e. the macroclass).
For instance we could classify grass (e.g. ID class = 1 and Macroclass ID = 1) and trees (e.g. ID class = 2 and Macroclass ID = 1) as a vegetation class (e.g. Macroclass ID = 1). If the option Use Macroclass ID is unchecked, then the classification is performed using the ID class only (e.g. grass and trees are classified as class 1 and 2 respectively).
The option Use Macroclass ID is also valid for classification previews and vector conversion.
If you do not need the macroclass, simply leave the Macroclass ID = 1 and the option Use Macroclass ID unchecked.
Each Class ID must be assigned to only one Macroclass ID (i.e. each class can have only one macroclass), but several Class IDs can be assigned to the same Macroclass ID (i.e. different classes can have the same macroclass). Of course, several ROIs can share the same Class ID.
The following images illustrate the classification differences between the use of Class ID and the use of macroclass ID.
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| Classification using the Class ID |
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| Classification using the Macroclass ID |
Finally, a new tab in the Main interface allows for the calculation of the ROI scatter plots, which are useful to assess ROI separability. Pixel values for two raster bands are represented as points in the 2D space.
It is possible to choose which ROI and which bands are shown in the plot.
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| Scatter plot tab |