Function circle 

pub fn circle(
    center: &GeoCoord,
    radius_m: f64,
    segments: usize,
) -> Vec<GeoCoord>

Generate a circle as a closed polygon ring.

Arguments

• center – centre of the circle.
• radius_m – radius in meters.
• segments – number of line segments (more = smoother). Clamped to a minimum of 4.

The returned ring is closed (first == last) and counter-clockwise.