Hexagons

// Hexagon polygon coordinates

extension TurbulenceItem {

  var hexagonCoordinates: [CLLocationCoordinate2D] {
  
    let center = self.coordinate
    let lngNorthWest = self.bbox[0] // bbox is 4 points in corners order: left top, right top, right bottom, left bottom

    let leftPoint = CLLocationCoordinate2D(
        latitude: center.latitude,
        longitude: lngNorthWest)
    let radius = CLLocation(coordinate: center)
        .distance(from: CLLocation(coordinate: leftPoint))
         
    let sidesCount = 6
    let shapeCoords = center.polygon(radius: radius, sidesCount: sidesCount)

    return shapeCoords
  }
}


// Helpers

extension CLLocationCoordinate2D {
    
    // self is center
    func polygon(radius: CLLocationDistance,
                 sidesCount: Int) -> [CLLocationCoordinate2D] {
        
        let stepDegrees: Double = 360 / Double(sidesCount)
        var coords: [CLLocationCoordinate2D] = []
        for i in 0...sidesCount {
            
            let coord = shift(byDistance: radius,
                              azimuth: degreesToRadians(degrees: stepDegrees * Double(i)))
            coords.append(coord)
        }
        return coords
    }
}


extension CLLocationCoordinate2D {
    
    /// Get coordinate moved from current to `distanceMeters` meters with azimuth `azimuth` [0, Double.pi)
    ///
    /// - Parameters:
    ///   - distanceMeters: the distance in meters
    ///   - azimuth: the azimuth (bearing)
    /// - Returns: new coordinate
    
    func shift(byDistance distanceMeters: Double, azimuth: Double) -> CLLocationCoordinate2D {
        
        let bearing = azimuth
        let origin = self
        let distRadians = distanceMeters / (6372797.6) // earth radius in meters
        
        let lat1 = origin.latitude * Double.pi / 180
        let lon1 = origin.longitude * Double.pi / 180
        
        let lat2 = asin(sin(lat1) * cos(distRadians) + cos(lat1) * sin(distRadians) * cos(bearing))
        let lon2 = lon1 + atan2(sin(bearing) * sin(distRadians) * cos(lat1), cos(distRadians) - sin(lat1) * sin(lat2))
        return CLLocationCoordinate2D(latitude: lat2 * 180 / Double.pi, longitude: lon2 * 180 / Double.pi)
    }
}