ILWIS objects |
Sample sets |
A sample set stores training pixels for supervised classification. Prior to an image classification, sample pixels or training pixels have to be selected in a sample set. A map list, containing the set of images used for classification and a background map on which you can locate training pixels and a class domain have to be specified. Then, during sampling, class names need to be assigned to groups of pixels that are supposed to represent a known feature on the ground and that have similar spectral values in the maps in the map list. A sample set is used as input in the Classify operation.
A sample set consists of:
When your graphics board is configured to use 256 colors, you can locate your training pixels on a background map, for instance a color composite. In case your graphics board is configured to use more than 256 colors, you will use an interactive color composite; then, a background map is not used.
Names of a sample set:
In ILWIS 3, object names comply with Windows long file names. Also Universal Naming Convention (UNC) paths are supported. For more information, see How to use long object names.
To create a sample set:
A sample set can be created by for instance double-clicking the Sample Map item in the Operation-list, or select Sample from the Operations menu, Image Processing. For other methods, see How to create a sample set. The sample set editor is opened.
Editing a sample set:
The easiest way to edit an existing sample set is by double-clicking it in the Catalog. See also, How to edit a sample set. For other methods, see How to edit a sample set. The sample set editor is opened.
Technical information:
A sample set consists of an ASCII object definition file (.SMS). This file contains further references to a domain (containing the class names of sampled pixels), a map list (containing the satellite bands), an optional background map, and to a raster map that is automatically created, with the same name as the sample set, and which contains the locations of training pixels and class names assigned to them (this map is called the sample map).
By viewing the properties of a sample set, you can see the domain, the name of the sample map, and the name of the map list that are used by the sample set; if your screen is configured for 256 colors only, also the background map used by the sample set is listed. These are properties of the sample set.
Limitations:
The maximum number of raster maps that can be included in a map list is 100 million. In practice however limitations will occur by available memory and disk space.
See also: