Function loop_signed_area 

pub fn loop_signed_area<'a>(
    pcurves: impl IntoIterator<Item = &'a NurbCurve2D>,
) -> GeopResult<Scalar>

The signed area the closed loop pcurves encloses, in order: positive counter-clockwise, negative clockwise (see the module docs).

Measured from the loop’s first point, sharpened: where the parts are measured from is a free choice, and one near the loop keeps the large correlated products of a loop far from the origin out of the integrand.