identify the shape of polygon

DanielSørensen

Hi everbody, I have a dataset contains polygon in a geodatabase, some of a shape of a circle like this:

and some squard like this:

 

Do you guys know a method, that can identify, what kind of shape the polygons are? I tried count the number of vertex's, which indicate a bit the shape (a high number of vertex indicate a circle - but not always). 

JohannesLindner

Hmmm, interesting.

4 vertices and distance(v1, v3) ~ distance(v2, v4): rectangle, else irregular quadrangle.

(Almost) circles: for each vertex, get the distance from the centroid. get min and max distance. if max - min ~ 0: it's a circle, else it's something else.

or: calculate the isoperimetric quotient of the polygon (https://en.wikipedia.org/wiki/Isoperimetric_inequality, https://en.wikipedia.org/wiki/Polsby%E2%80%93Popper_test😞

Q = 4*pi*area/(perimeter^2)

For Q == 1 it's a circle; the lower Q gets, the less circle-ish the shape is.

 

rectangle-ish shapes with more than 4 vertices: get bearing of each line segment. if bearing[i] ~ bearing[i+1], it's the same side. if you get 4 sides this way, you know its a quadrangle. get the angles between the sides. if they're ~90°, it's a rectangle.