Function robust::incircle

pub fn incircle<T: Into<f64>>(
    pa: Coord<T>,
    pb: Coord<T>,
    pc: Coord<T>,
    pd: Coord<T>
) -> f64

Returns a positive value if the coordinate pd lies inside the circle passing through pa, pb, and pc.
Returns a negative value if it lies outside the circle.
Returns 0 if the four points are cocircular.
Note: The points pa, pb, and pc must be in counterclockwise order, or the sign of the result will be reversed.