Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: method name
OSC_VECTOR2D_VALUE_METHOD_NAME
Parameter: set
OSC_VECTOR2D_VALUE_SET_METHOD_NAME
Parameter: x
OSC_VECTOR2D_VALUE_X
Parameter: y
OSC_VECTOR2D_VALUE_Y
Parameter: OSC_VECTOR2D_VALUE_PORT_X
OSC_VECTOR2D_VALUE_PORT_X
Parameter: OSC_VECTOR2D_VALUE_PORT_Y
OSC_VECTOR2D_VALUE_PORT_Y