Network and Dynamic Segmentation

1. Network and Dynamic Segmentation Chapter 16

2. Introduction • A network consists of connected linear features. • Dynamic segmentation is a data model that is built upon lines of a network and allows the use of real-world coordinates with linear measures such as mileposts. • Both models must have the appropriate attributes for real-world applications.

3. Introduction • ARC/INFO can work with both network and dynamic segmentation • ArcView with Network Analyst can do network model

4. Network • A network is a line coverage, which is topology-based and has the appropriate attributes for the flow of objects such as traffic. • Examples: links, turns, one-way streets, overpass, underpass; impedance

5. Link Impedance • Link impedance: measure of the cost of traversing a link; cost rather than length, such as travel time (30 vs 10 mph). • Directional differences (to-from node) • Time of day • Day of week

6. Turn Impedance • Transition from one arc to another • Time to make the turn • Turn table because of changing conditions; node number, arc numbers, turn impedance • Straight, left, right, possibly U • Usually directional • Negative impedance for prohibited activity

7. Putting Together a Street Network • Preliminary coverage from TIGER, convert to real world coordinates. • Edit and update: attributes, new/changed streets, pseudo nodes for attributes change. • Add impedance values. • Consistent one-way streets and directions • Create turn table

8. Network Applications • Shortest Path Analysis • path with minimum cumulative impedance between nodes • in-vehicle Route Guidance System (RGS) • Traveling salesman problem • more complex • must visit each one time • must return to original stop • Many algorighms

9. Network Applications • Shortest Path Analysis • ARC/INFO has PATH and TOUR • ArcView Network Analyst has “Find Best Route” • Both create a route and option of providing directions

10. Network Applications • Closest Facility • Computes shortest paths from the selected location to all candidate facilities and then chooses the closest facility

11. Network Applications • Allocation • Study of spatial distribution of resources through a network • Often refer to public facilities service zones • Efficiency is response time • Location-Allocation • Minimize use of resources using facilities and at the same time meeting objectives

12. Network Applications • Maximum covering model • maximizes the demand covered within a specified time or distance. • Urban Transportation Planning Model • typically uses four-step process of trip generation, trip distribution, modal choice, and trip assignment • complex, must have arc-node topology

13. Dynamic Segmentation • Built upon arcs of a network • Basic elements of routes, sections, and events • Route is a collection of sections and resides in a line coverage as a subclass • Section refers directly to arcs in the line coverage and provides measures to route system • Events are occurrences related to the route system

14. Creating Routes • On new arcs • On existing Arcs • Different types of routes • simple (one direction without loop or branch) • combined (route is joined by another route) • split route (route subdivides into two routes) • looping route (route intersects itself)

15. Event Tables • Events are attribute data measured on a linear reference system • point events, such as accidents and stop signs • continuous events, such as speed limits (always present) • linear events, such as pavement conditions (off and on situations)

16. Applications of Dynamic Segmentation • Display, query, and analysis of routes, measures, and events. • Analysis of accidents • Changes