Function robust_geo::in_circle

pub fn in_circle(
    a: Vector2<f64>, 
    b: Vector2<f64>, 
    c: Vector2<f64>, 
    d: Vector2<f64>
) -> f64

Returns a positive number if d is inside the oriented circle that goes through a, b, c, a negative number if it lies outside, and 0 if a, b, c, d are cocircular or a, b, c are collinear. If a, b, c are in counterclockwise order, "inside the circle" is the inside. If a, b, c are in clockwise order, "inside the circle" is the outside.