Function init_camera 

pub fn init_camera(
    model: CameraModelKind,
    width: u64,
    height: u64,
    exif: &ExifInfo,
    params: Option<&[f64]>,
    default_focal_length_factor: f64,
) -> Result<Camera>

Initializes a new camera: uses params as-is if given (flag set); otherwise EXIF/default focal length

• principal point (W/2, H/2), zero distortion.