How to create
a sample set for image classification
To perform an image classification, a sample set has to be created. Then, you can sample training pixels: assign class names to groups of pixels with similar spectral values and that are supposed to represent a known feature on the ground.
A sample set consists of:
- a reference to a map list, that is the set of images you want to classify in a later stage; the images in the map list are used to extract sample statistics during sampling and display these in feature spaces,
- a reference to a class domain, that is the collection of class names that you want to assign to your training pixels,
- a reference to a sample set raster map which is automatically created and obtains the same name as the sample set; this map contains the locations of the training pixels and the class names assigned to them.
- when your graphics board is configured to use 256 colors, a reference to a background map, that is the map on which you can locate your training pixels; this background map can for instance be a color composite.
Tip:
When your graphics board is configured to use more than 256 colors, you will use an interactive color composite; then, a background map on disk is not used. For more information, refer to How to create a color composite.
To create a sample set:
- from the File menu in the Main window, choose Create Sample Set, or
- in the Operation-tree, open the Create item, and double-click the New SmplSet item,
- in the Operation-list, double-click the item New SmplSet, or
- from the Operations menu in the Main window, choose Image Processing, Sample, or
- in the Operation-tree, open the Image Processing item, and double-click the Sample Map item, or
- in the Operation-list, double-click the Sample Map item.
By the first two actions, the Create Sample Set dialog box will appear. In the this dialog box, you can specify the sample set's name, and the domain, map list, and background map that you want to use during sampling.
By the last two actions, the Sampling dialog box appears in which you can select an existing sample set, for instance to add more training pixels, but you can also create a new sample set by clicking the little create button. If the create button is used, the Create Sample Set dialog box will follow.
When everything is OK, the sample set editor is started which allows you to select training pixels, show feature spaces, etc.
See also:
ILWIS objects : sample sets
How to create a map list
How to create a color composite
Sample set editor