$$PARA_{CV} = cv(PARA[patch_{ij}]$$
where \(PARA[patch_{ij}]\) is the perimeter area ratio of each patch.
PARA_CV is a 'Shape metric'. It summarises each class as the Coefficient of variation of
each patch belonging to class i. The perimeter-area ratio describes the patch complexity
in a straightforward way. However, because it is not standarised to a certain shape
(e.g. a square), it is not scale independent, meaning that increasing the patch size
while not changing the patch form will change the ratio.
Behaviour
Equals PARA_CV = 0 if the perimeter-area ratio is identical for
all patches. Increases, without limit, as the variation of the perimeter-area ratio
increases.