Χρήση συστημάτων πληροφορικής στην οδική υποδομή

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1 ΕΘΝΙΚΟ ΜΕΤΣΟΒΙΟ ΠΟΛΥΤΕΧΝΕΙΟ ΕΜΠ Εργαστήριο Συγκοινωνιακής Τεχνικής Χρήση συστημάτων πληροφορικής στην οδική υποδομή Βύρωνας Νάκος Καθηγήτης ΕΜΠ Εφαρμογές δεδομένων που αναφέρονται σε δίκτυα

2 Άδεια χρήσης Το παρόν εκπαιδευτικό υλικό υπόκειται σε άδειες χρήσης Creative Commons. Για εκπαιδευτικό υλικό, όπως εικόνες, που υπόκειται σε άδεια χρήσης άλλου τύπου, αυτή πρέπει να αναφέρεται ρητώς. 2

3 Συστήματα Γεωγραφικών Πληροφοριών & Μεταφορές Εφαρμογές δεδομένων που αναφέρονται σε δίκτυα Βύρωνας Νάκος, Καθηγητής Ε.Μ.Π.

4 Contents How a roadway is represented within GIS Characteristics of Routes Routes & network topology Road networks & generalization Linear location referencing system & accuracy Route calibration Dynamic segmentation

5 How a roadway is represented within GIS In GIS a roadway is represented as a collection of lines with endpoints defined in coordinate space A combined collection of graphical links form a roadway network, but this representation alone is considered as having no intelligence. That is, connectivity and designated route topology are not present Routes Are special feature types constructed from the roadway line features (e.g., route number) and can be designated in GIS using relational database tables to identify those lines that make up each route

6 Characteristics of Routes Routes also have a linear location referencing method associated with them that allows event locations (i.e. crash location milepoint) to be positioned on the route To implement this capability in GIS, route measures are assigned as attributes to the route at the starting, ending, and intermediate points along the route The intermediate route measures are used to control location placement accuracy for events along the route

7 Routes & network topology GIS has historically relied on a cartographic data model to represent roadways and other feature elements GIS uses a coordinate system to store and display primitive feature elements of points, lines, and areas In the cartographic data model a roadway is represented as a line feature GIS builds and manages topology in the cartographic model A road network (Routes) is the connection of a series of roadway line features having the same defined attributes. This interconnectivity of line features is important for using routing applications or in network data modeling Appropriate connectivity and related information can be designed and built into the GIS data to develop the network data model for the support of network analysis

8 Road networks & generalization Modeling the road network as a spatial layer in GIS is a planning exercise that needs to be compatible with and reflect the needs and requirements of the application Mainline, secondary routes, collectors, and interchange features can be represented in GIS at various levels of detail It is important to understand the difference between small-scale and large-scale mapping

9 Linear location referencing system & accuracy For road network applications GIS brings together data from various sources: the GIS roadway network the linear location referencing system s event database and the linear location referencing system s roadway inventory data When merging data from different sources, the least accurate data source is used for determining overall data accuracy The accuracy of linear referenced data is relative to, and thus mostly dependent on, the calibration of route measures along the road network, and less dependent on the accuracy of the road network data in GIS

10 Why route calibration? The real world, however, is three-dimensional In three dimensions topography also affects the distance along a roadway The measurements taken by field personnel are obviously made in the real world and, therefore, accurately record distances as they are measured along both horizontal and vertical curves These measurements reflect the geographic accuracy of a roadway and are the distances used to reference features in an linear location referencing system

11 Route calibration Regardless of the source of the error, differences between the distances measured in the field and those calculated by the GIS software will make it difficult to precisely locate attributes and events referenced by an offset from a node or from the route s origin on a two-dimensional map When the GIS lengths differ from the actual distances as measured in the field, events can float away from their actual linear location The process of adjusting the two-dimensional GIS link lengths based on three-dimensional field measurements taken at control points (points at known distances along the route) is known as route calibration

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13 Route calibration using control points The process of route calibration effectively shifts points referenced by an offset along a specified route closer to their actual location Associating accurate cumulative distance measurements of known, observable features to points on the graphic representation in GIS causes GIS to know the three-dimensional mileage These points in GIS of known three-dimensional cumulative measurements are known as control points A control point is one with a known set of coordinates and a known real-world distance from another control point (e.g., the beginning of a route or an intersection) The GIS software automatically shifts points in between control points, or intermediate points, proportionately to the shift of the node to its control point

14 Route calibration using control points d D i i d D cp cp Where d i : Calibrated distance from point i D i : Calibrated distance between control points d cp : Measured distance from point i D cp : Measured distance between control points

15 Dynamic segmentation Dynamic segmentation is the process of computing the locations of events stored and managed in an event table using the measurements of a linear location referencing system which are projected on the representation of the road network as it is provided by a GIS The term dynamic segmentation is derived from the concept that line features need not be split (i.e., segmented) each time an attribute value changes Using dynamic segmentation, multiple sets of attributes can be associated with any portion of an existing linear feature independently of where it begins or ends These attributes can be displayed, queried, edited, and analyzed without affecting the underlying linear feature's geometry

16 The importance of dynamic segmentation is that the virtual network of routes and associated data is non-topological, and thus avoids many of the limitations of the Link-Node network model

17 References Bernhardsen T., 2002, Geographic Information Systems. An Introduction (3rd ed.), New York: John Wiley & Sons. Boston S., 2011, Harmonisation of Location Referencing for Related Data Collection, Sydney: Austroads Publication No. AP T Miller H.J. & Shaw S.-L., 2001, Geographic Information Systems for Transportation: Principles and Applications, Oxford: Oxford University Press. Sutton J., 1998, Data attribution and network representation issues in GIS and transportation, Transportation Planning and Technology, 21(1-2): Trentacoste, M.F. (ed.), 2001, Implementation of GIS-Based Highway Safety Analyses: Bridging the Gap, Report No. FHWA-RD , McLean: U.S. Department of Transportation, Federal Highway Administration.

18 Χρηματοδότηση Το παρόν υλικό έχει αναπτυχθεί στα πλαίσια του εκπαιδευτικού έργου του διδάσκοντα. Το έργο υλοποιείται στο πλαίσιο του Επιχειρησιακού Προγράμματος «Εκπαίδευση και Δια Βίου Μάθηση» και συγχρηματοδοτείται από την Ευρωπαϊκή Ένωση (Ευρωπαϊκό Κοινωνικό Ταμείο) και από εθνικούς πόρους. 1