A categorical raster object: SpatRaster; Raster* Layer, Stack, Brick; stars or a list of SpatRasters.
directions
The number of directions in which patches should be
connected: 4 (rook's case) or 8 (queen's case).
Details
$$FRAC_{MN} = mean(FRAC[patch_{ij}])$$
where \(FRAC[patch_{ij}]\) equals the fractal dimension index of each patch.
FRAC_MN is a 'Shape metric'. The metric summarises the landscape
as the mean of the fractal dimension index of all patches in the landscape.
The fractal dimension index is based on the patch perimeter and
the patch area and describes the patch complexity. The Coefficient of variation is
scaled to the mean and comparable among different landscapes.
Because the metric is based on distances or areas please make sure your data
is valid using check_landscape.
Units
None
Range
FRAC_MN > 0
Behaviour
Approaches FRAC_MN = 1 if all patches are squared and FRAC_MN = 2
if all patches are irregular.
References
McGarigal K., SA Cushman, and E Ene. 2023. FRAGSTATS v4: Spatial Pattern Analysis
Program for Categorical Maps. Computer software program produced by the authors;
available at the following web site: https://www.fragstats.org
Mandelbrot, B. B. 1977. Fractals: Form, Chance, and Dimension.
San Francisco. W. H. Freeman and Company.