Autocorrelation - Semivariance

Dialog box

AutoCorrelation calculates autocorrelation and semi-variogram values for a raster map. The autocorrelation of a raster map is generated by calculating the correlation between pixel values of a raster map and pixel values of the same raster map for different shifts (lags) in horizontal or vertical directions. The semi-variogram values which are a measure of the spatial variability within a raster map are calculated for the same shifts. The operation is a tool to obtain information on horizontal and vertical patterns in a raster map.

Dialog box options:

Input raster map:

Select an input raster map. Open the list box and select the desired input map, or drag a raster map directly from the Catalog into this box. The raster map need to be a value map.

Maximum pixel shift:

Type a value for the maximum pixel shift (in pixels), i.e. the maximum separation distance between pixels until which correlation and semi-variogram values should be calculated. By making a graph of distance against for instance output experimental semi-variogram values, you can find until which distance, the values in the raster map are related to each other (in geostatistics, that distance is called the range).
The smallest possible value which you can enter is 1 (shift of 1 pixel). The largest value which is accepted is the number of rows in the map or the number of columns in your map (the largest of these). For very large maps, the maximum pixel shift is furthermore limited to 8000.

Output table:

Type a name for the output table that will contain the autocorrelation and the experimental semi-variogram values for shifts of 1 pixel, 2 pixels, 3 pixels, etc. until the specified maximum pixel shift.

Description:

Optionally, type a description for the output table. The description will appear in the status bar of the Main window when moving the mouse pointer over the table in a Catalog, and in the title bar of a table window when the output table is displayed. If no description is supplied, the output table will use its own definition as description.

When you click the Show button, the dependent output table will be defined, calculated and shown. When you click the Define button, the dependent output table will only be defined; if necessary the table will be calculated later, for instance when the table is opened to be displayed.

See also: