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
$$SHAPE = \frac{0.25 * p_{ij}} {\sqrt a_{ij}}$$
where \(p_{ij}\) is the perimeter (m) and \(a_{ij}\) is the area (m2).
SHAPE is a 'Shape metric'. It describes the ratio between the actual perimeter of
the patch and the square root of patch area and thus adjusting for a square standard.
Thus, it is a simple measure of shape complexity.
Units
None
Range
SHAPE >= 1
Behaviour
Equals SHAPE = 1 for a squared patch and
increases, without limit, as the patch shape becomes 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.