A = geom.signedarea (P) returns the signed area of the polygon whose vertices are the rows of the $N$-by-2 matrix P, in the square of the unit of P. Package convention is millimetres, so the area is in square millimetres.

The polygon is implicitly closed: the last vertex joins the first. An explicitly repeated closing vertex is accepted and ignored.

The sign carries the orientation. A is positive when the vertices run counter-clockwise and negative when they run clockwise, so sign (geom.signedarea (P)) is the cheapest orientation test available, and abs of the result is the plain area.

The result is meaningful only for a simple polygon, that is, one whose edges do not cross. Self-intersecting input returns a number, but not one that means anything.

See also: geom.bbox, geom.centroid, geom.isrectilinear

Source Code: geom.signedarea