[feature] : Circularity Metric

[MaxGamill-Sheffield]

Is your feature request related to a problem?

Aim is to have a measure of circular-ness or roundness output in the grainstats.

Describe the solution you would like.

Can be done by measuring the grains outer hull and using a ratio of its area to its perimeter (or circumference):

Roundness = 4π × Area / Perimeter^2

Will give a normalised value of 0 for non-circles and 1 for a perfect circle.

Describe the alternatives you have considered.

No response

Additional context

No response

[SylviaWhittle]

Note: A couple other similar metrics that have been used in the past are:

ratio of feret diameters - since a circle has a feret ratio of 1 and a line has a feret ratio of big. But this metric can be gamed.

Variance in distances of edge points from centroid

Though the geometrically derived metric above is likely the best in most cases