boost::optional<Timestamp> left_time, right_time;
const set< shared_ptr<SignalData> > visible_data = get_visible_data();
for (const shared_ptr<SignalData> d : visible_data) {
boost::optional<Timestamp> left_time, right_time;
const set< shared_ptr<SignalData> > visible_data = get_visible_data();
for (const shared_ptr<SignalData> d : visible_data) {