Transcript Geometric Networks in ArcGIS Sewer, water, roads, etc.. 2/2008 GISC 6382 UT-Dallas Briggs.

Geometric Networks in ArcGIS
Sewer, water, roads, etc..
2/2008
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Types of Networks
Networks are of two types
– Directed flow (geometric networks)
• utility networks such as sewer and water systems; rivers and streams
• Elements on the network have no choice in travel decision. Flow
direction is determined by the network characteristics alone.
• Referred to as geometric or utility networks by ESRI
• Available with ArcEditor level of ArcGIS
– Undirected flow
• Transportation networks such as streets
• Elements on the network make their own travel decisions. Flow
direction not determined solely by network.
• Available thru Network Analyst extension
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Geometric Networks and Network Topology
Geometric Networks can also be useful for checking network
topology
– provide an alternative approach to applying topology rules
• checking editing on a line file for connectivity and overlaps
• Linking points and lines into a topological structure
• Network Topology
– a procedure for ensuring the integrity of data
– applying topology rules for points and lines feature classes
– examined in av9edit_topo.doc
• Geometric (Utility) Network
– a procedure for modeling flows thru a network
– However, can also be helpful in editing network data and ensuing its
integrity
My guess is that each was developed by separate teams with
different primary goals, with overlap occurring in the process
Note 1: If a Topology relationship class exists in a feature dataset, you
cannot build a geometric network.
Note 2: ArcEditor is required for either.
Creating a Network in ArcCatalog
• Geometric networks are created in ArcCatalog and
stored as a relationship class within a geodatabase
feature dataset
– Right click on a feature dataset and select
New/Geometric network to start the wizard for
creating the network
– The network (a relationship class) and its junctions (a
point feature class) are listed along with the feature
classes
• Multiple point and line feature classes can participate in a network but
they must all be in the same feature dataset
– However, not all line or point feature classes in the feature dataset have to
participate
– The features within participating feature classes
• May be moved if snapping is allowed
• Have one or two new attribute fields: Enabled and Ancillary Role (if Source/Sink)
– A feature class can only participate in one network
• If desired, you can create a network with empty feature classes, and
populate by editing in ArcMap, or loading data
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Analyze Network in ArcMap
what you can do with a network
• relate lines and points together so that when a move is performed in editing all
points and lines move together
• Establish flow direction in network using sources and sinks
sink
down the network to a sink
or down the network from a source
source
– Intended for tracing paths through network
– Also useful to find errors in edited files (lines not snapped together, etc..)
– Sources and sinks are identified in the AncillaryRole field in the point feature
class(es). A junction is either: source, sink, none, Usually have only sources or sinks
• Restrict flow via barriers, and observe effect on trace
(pipe clog, pipe break, etc..)
– Temporary barriers applied to junction or edge with Barrier tool in map document
(e.g pipe break now)
– Semi-permanent barriers applied through the Enabled field in point or line feature
classes in database (e.g pipe segment under construction)
• Perform network analyses (e.g. find common ancestor, find connected segments)
– Junction or edge Flags are the starting point for these various trace operations
All are implemented with the Utility Network Analyst toolbar
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Key Concepts
• Networks are made up of:
– Edges (derived from Line feature classes)
edges
• These have distance and direction
junctions
– Junctions (derived from Point feature classes)
• All edges end at a junction
• Junctions may be end point of a line or intersections between lines
• If a point from a point feature class is not available to serve as a junction, a
point, called an orphan junction, is created in the junction feature class
• Edges and Junctions may be simple or complex
Complex
– Simple edges/junctions consist of a single feature
edge
– Complex edges allows edges to connect without separate segments
– Complex junctions represent multiple features
Simple
edge
• A pump station complex junction may itself consist of multiple water lines
(edges) and valves (junctions)
• Weights may be associated with both edges and junctions
– They represent the cost of traveling over that feature
– They are calculated based upon an attribute of the feature (e.g. length of6
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a pipe segment)
Type of network flow
• Uninitialized
– Flow has not yet been set for this part of the network
• Determined
– Flow has been set for this part of the network
• Undetermined
– Flow cannot be determined for this part of the network
given the sources and sinks that are established
– Acts the same as uninitialized flow
– Same symbol used as default,
but can be changed via options
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Building and Using the
Geometric Network
Reference detail
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Building the network
• Select a feature dataset
• Name your network
• Select feature classes to
participate
• Set snapping
– Tolerance distance
– Feature classes to snap to
• Identify complex edge
feature classes
• Define Sources and Sinks
• Set weights
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Define Source and Sinks
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Establishing flow with sources and sinks
• Flow goes from source to sinks
• AncillaryRole field of junctions
– A domain defines the available values
• None
• Source
• Sink
– Recalculate flow after editing and before
analysis with
tool
– Display flow arrows via Flow/Display Arrows
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Network Weights
Cost to traverse an edge or junction
• Based on numeric field values
– Lower numbers = lower resistance
– Can be bidirectional (two way) by using two fields
• Negative values are barriers
– block flow down that segment
• Define when the network is created
– Name the weight
– Apply it to a field in one or more feature classes
(process similar to using a domain: “define” then “apply”)
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Add Weights to a network
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Add complex edges and
Define feature to be snapped
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Network Analysis
• Network Traces
–
–
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–
Tracing upstream and downstream
Finding path
Finding common ancestor
Find connected
• Flags are use to define locations for tracing: 3 step process
– Place the flags
– Choose a trace task
– Solve the trace
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Tracing upstream and
downstream
• Upstream trace
• Downstream trace
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Finding Path
• Find the best path between two flags
– Upstream, downstream, connected
– From first flag to second flag
• Flags are placed on any feature
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Finding common ancestor
• Piece of upstream network common to all
flags
– Which electric line is common to all house?
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Finding connected features
• Finding features connected to a flag
• Commonly used for isolating features
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Disable layer(s) (e.g. Valves)
Set Trace to Ends Property
Place a flag on the feature you want to isolate
Trace back to the disable layer
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Finding Indeterminate Flow
• Use the Find Loops analysis
No Cycle (switch open)
Cycle (switch closed)
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Connectivity Rules for Networks
• similar to domains for geodatabases
– Domains control the values that variables can assume
• Can apply at subtype level and also set default values
– Connectivity rules allow you to control:
• which edges may connect together
• what junctions (points) must be used to connect these edges
• Can apply at subtype level and also set default values
– Two types
• Edge to junction rules
• Edge to edge rules
– Cardinality
• The number of features that can connect
• Number of edges a junction can connect to
• Number of junctions an edge can connect
Setting Connectivity Rules
• Connectivity rules are network versions of
domains
– “business rules” which you apply to connections
between features
• By default, all features can connect
– Setting one rule means you have to set rules for
everything you want to connect
– This can be a lot of work!
• Connectivity rules are set after the network is
created by right clicking the network relationship
class in ArcCatalog and going to
Properties/Connectivity tab
– Another option is to select Geometric Network Editor
instead of going to Properties. (Probably easier once
concept is understood)
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Setting Edge-to-Junction rules
(and junction-to-edge)
This feature class
(edge, in this case)
With these
Cardinalities
With this subtype
Connects to
this junction
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Setting Edge-to-Edge Rules
This Edge
Connects to
this edge
Through this
junction
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