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Network Analysis in ArcInfo 8.0

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  1. Network Analysis in ArcInfo 8.0

  2. Topics • Network Data Model • Network Flow • Weights • Solvers

  3. Network Data Model

  4. Network data model • Geometric and Logical views • Geometric and Logical Networks • Edge and junction features and elements • Simple edges • Complex edges and junctions

  5. Two Views of Networks Geometry and Connectivity

  6. Two views of Networks

  7. Geometric and Logical Networks • The Geographic view is implemented as a Geometric Network • a collection of feature classes in a feature dataset • The Logical view is implemented as a Logical Network • a specialized data structure for storing connectivity

  8. Understanding the relationship • Understanding the correspondence between the geometric and logical network is very helpful • Developers writing analysis programs deal almost exclusively with the Logical Network • Database designers, data builders, and analysts can all benefit from an understanding of this correspondence

  9. Geometric Networks • Binds together feature classes that make up a network • Edge and Junction Features • Contains all network validation rules, relationships, attributes • Used for display and editing • Easily created with a wizard

  10. Geometric Networks Network Feature Classes Valve Meter Lateral Geometric Network DistMain TransMain

  11. Geometric Network in ArcCatalog

  12. Logical Networks • Store network connectivity • Maintained by Geometric Network • Behind the scenes - not shown in ArcCatalog • Network analysis programs use logical networks • Very high performance engine

  13. Always maintained • The Geometric and Logical networks are always “in sync”, always “live” • No separate building and maintaining of network • Geometric Network maintains Logical Network • Smart network features

  14. The centerpiece of a logical network is the connectivity table

  15. Simple Network Features • One-to-one correspondence between features and elements

  16. Simple Network Features • Single main servicing two houses • Connecting two simple junctions to simple edge results in three simple edges • one-to-one mapping

  17. Complex Edges • One-to-many mapping between feature and edge elements • Connecting junction does not cause split • Complex edge may only be split with Split tool

  18. Complex Edges • Note one-to-many feature to edge element mapping using Sub-ID

  19. Complex Junctions • Single feature that is mapped to any number of edge and junction elements • Fixed topology • Utilizes connection points for establishing connectivity • Switchgear example

  20. Complex Junctions • In this example, the switchgear is modeled as • four edge elements • five junction elements

  21. Network Flow • Operational context • Establish Flow Direction • Flow direction part of Logical Network • Sources, Sinks, enabled/disabled state • Indeterminate and Uninitialized flow

  22. Two operational contexts • In a street network, the commodities (automobiles) that flow through a network have a “will of their own”, and decide how they’ll flow through the network. • In a utility network, the commodities (water, electricity) have no will of their own, and the network imposes a flow direction.

  23. Street and Utility Networks • Street networks have non-directed flow • Utility networks have directed flow

  24. Establishing Flow Direction • A Utility network has an Establish Flow Direction Method, which determines the direction of flow along each edge element • Flow direction stored with Logical Network

  25. Sources and Sinks • The Establish Flow Direction method uses sources and sinks • Sources and sinks are stored with the logical network • Implemented with Attribute Domains on Geometric Network

  26. Enabled/Disabled state • Every element has an enabled/disabled state. • Implemented with attribute domains on Geometric Network. • The state found on features applies to all elements. You cannot turn off a portion of a complex edge.

  27. Indeterminate Flow • It may not be possible to establish flow direction, typically due to cycles

  28. Uninitialized flow • A network may have disconnected components - sets of elements that don’t connect to other sets • When a component cannot be reached by any source or sink, its flow is uninitialized

  29. Weights • Features and elements can have any number of weights • Editing weight values in a network feature class table automatically updates the logical network

  30. Weights • Weights on different classes can be mapped to single weight in logical network

  31. Bitgate Weight • Used for categories • In this example, categories of vehicles are represented

  32. Creating Geometric Networks • May use ArcCatalog or ArcToolbox • Use the New Geometric Network tool in the context menu • only on a feature dataset

  33. Building Geometric Networks • Use wizard to specify • input feature classes • complex edges • snapping • ancillary roles • weights

  34. Network Feature Classes • May add new feature classes to existing network • Use the New Feature Class tool in the context menu

  35. Network Feature Classes • Choose a network feature type • ESRI Simple Junction • ESRI Simple Edge • ESRI Complex Edge • Custom • Choose network • Specify ancillary role

  36. Network Analysis • Solvers • Flags • Barriers • Trace Solvers • Demos

  37. Solvers • Solvers are programs that use a logical network to solve a problem • Numerous network problems = numerous solvers • Our strategy is to provide a rich suite of solvers that address the more common types of problems • Extensible environment to plug in solvers

  38. Example solver written in Visual Basic • Implements a TraceTask solver • Plugs into ArcMap’s Utility Network Analysis Toolbar Implements ITraceTask . . .Private Function ITraceTask_OnTraceExecution() As esriCore.IEnumNetEID 'Check to make sure we have an edge flag set Dim m_pFlags As IFlagsAndBarriers Set m_pFlags = m_pTraceSolver If m_pFlags.EdgeFlagCount = 0 Then MsgBox "Set an edge flag before using this trace task" Set ITraceTask_OnTraceExecution = Nothing Exit Function End If 'Prepare for the trace Dim m_pNewTrace As ITraceFlowSolver Set m_pNewTrace = UTIL_CoreTraceSetup(m_pFlags) 'Make sure the solver came back If m_pNewTrace Is Nothing Then Set ITraceTask_OnTraceExecution = Nothing Exit Function End If 'Set the isolation layer Dim lIsolationFCID As Long Dim m_pTraceProperties As ITraceProperties Set m_pTraceProperties = m_pTraceSolver If m_pTraceProperties.IsolationLayerCount = 1 Then Dim iLoop As Integer lIsolationFCID = m_pTraceProperties.IsolationLayerFCID(CLng(iLoop)) For iLoop = 0 To m_pTraceProperties.IsolationLayerCount - 1 m_pNewTrace.DisableElementClass lIsolationFCID Next iLoop . .

  39. Solver Interfaces • Collections of solvers that perform similar tasks can usually be plugged into a common user interface framework • A toolbar for solving water network problems, one for telco, one for routing, etc. • ArcMap is part of a solver user interface • Similarly, collections can implement similar behavior • Support common program interface (I.e., ITraceTask)

  40. Solver inputs • Logical Network • Netflags • Barriers • Other parameters • weights

  41. Solver Outputs • Collections of edge and junction elements • Netflag collections • Other stuff • numbers, booleans

  42. Solver Renderers • Take solver output and displays in ArcMap • Converts element class ID, feature ID, and Sub-ID into geometry to display

  43. Netflags

  44. Barriers • Used to temporarily disable elements • Four ways to specify barriers • Simple barriers - a collection of junction and edge elements • Selected sets of features • Feature class • Bitgates

  45. Utility Network Analysis Toolbar • ArcMap Tool, accessed through the tool menu • Used to Establish Flow Direction and to perform Trace tasks • Six solvers • Three need to have flow direction established