Perspective_Projection.swift

    
    /**
        Calculate the x-pixel offset for an angle using perspective projection
        http://stackoverflow.com/questions/16619104/perspective-projection-in-android-in-an-augmented-reality-application
    
        - parameter angle: The viewing angle for the object
    
        - returns: xOffset CGFloat for the x location of the object on the screen
    */
    private func getXPerspectiveOffset(angle: Double) -> CGFloat {
        var xOffset = CGFloat(0.0)
        if currentHeading != nil && focalLen != nil {
            let viewAngle = degreesToRadians(angle - currentHeading!)
            xOffset = CGFloat(tan(viewAngle)) * CGFloat(focalLen!)
        }
        //Larger value = more to the right
        return xOffset + view.frame.width/2.0
    }
    
    /**
        Calculate the y-pixel offset for an angle using perspective projection
        http://stackoverflow.com/questions/16619104/perspective-projection-in-android-in-an-augmented-reality-application
    
        - parameter angle: The viewing angle for the object
    
        - returns: yOffset CGFloat for the y location of the object on the screen
    */
    private func getYPerspectiveOffset(angle: Double) -> CGFloat {
        var yOffset = CGFloat(0.0)
        if currentPitch != nil && focalLen != nil {
            let viewAngle = degreesToRadians(angle - currentPitch!)
            yOffset = CGFloat(tan(viewAngle)) * CGFloat(focalLen!)
        }
        //Larger value = lower
        return view.frame.height/2.0 - yOffset
    }