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
$$SHAPE_{MN} = mean(SHAPE[patch_{ij}])$$
where \(SHAPE[patch_{ij}]\) is the shape index of each patch.
SHAPE_MN is a 'Shape metric'. The landscape is summarised as the mean
of all patches in the landscape. SHAPE describes the ratio between the actual perimeter of
the patch and the square root of patch area.
Units
None
Range
SHAPE_SD >= 1
Behaviour
Equals SHAPE_MN = 1 if all patches are squares.
Increases, without limit, as the shapes of patches become more complex.
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
Patton, D. R. 1975. A diversity index for quantifying habitat "edge".
Wildl. Soc.Bull. 3:171-173.