set_view_between_frames Subroutine

    subroutine set_view_between_frames(self, root, frame, lookat, frame_type, rotation_type)
        class(View), intent(inout) :: self
        class(ReferenceFrame), intent(in), target :: root, frame, lookat !! the tree's root, viewed and looked-at frames
        integer, intent(in), optional :: frame_type         !! ABSOLUTE_FRAME or RELATIVE_FRAME (default)
        integer, intent(in), optional :: rotation_type      !! VIEW_DIRECT or VIEW_AZEL (default)
        self%root => root
        self%frame => frame
        self%lookat => lookat
        self%frame_type = RELATIVE_FRAME
        self%rotation_type = VIEW_AZEL
        if (present(frame_type)) self%frame_type = frame_type
        if (present(rotation_type)) self%rotation_type = rotation_type
    end subroutine set_view_between_frames