$$FRAC_{SD} = sd(FRAC[patch_{ij}])$$
where \(FRAC[patch_{ij}]\) equals the fractal dimension index of each patch.
FRAC_SD is a 'Shape metric'. The metric summarises each class
as the standard deviation of the fractal dimension index of all patches
belonging to class i. The fractal dimension index is based on the patch perimeter and
the patch area and describes the patch complexity.
Because the metric is based on distances or areas please make sure your data
is valid using check_landscape.
Behaviour
Equals FRAC_SD = 0 if the fractal dimension index is identical
for all patches. Increases, without limit, as the variation of the fractal dimension
indices increases.