void add_track(Track3D &);
void remove_track(Track3D &);
const TrackMap &get_tracks() const { return tracks; }
Track3D &get_track(Track &) const;
void add_track(Track3D &);
void remove_track(Track3D &);
const TrackMap &get_tracks() const { return tracks; }
Track3D &get_track(Track &) const;