Network analysis in gis , part 5 geometric network

Part 5 Geometric networks
Dr. IBRAHIM BATHIS K
https://www.linkedin.com/in/dribrahimbathisk/

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
Networks are of two types

Geometric Networks
 River networks and utility networks-like electrical, gas, sewer, and water
lines-allow travel on edges in only one direction at a time.
 The agent in the network-for instance, the oil flowing in a pipeline-
can't choose which direction to travel; rather, the path it takes is
determined by external forces: gravity, electromagnetism, water pressure,
and so on.
 An engineer can control the flow of the agent by controlling how
external forces act on the agent.
 A geometric network is a set of connected edges and junctions, along
with connectivity rules, that are used to represent and model the
behavior of a common network infrastructure in the real world.
 Geodatabase feature classes are used as the data sources to define the
geometric network.

Network datasets
 Transportation networks-like street, pedestrian, and railroad networks-can allow
travel on edges in both directions.
 The agent on the network-for instance, a truck driver traveling on roads-is
generally free to decide the direction of traversal as well as the destination.
 Network datasets are good for modelling undirected networks because they can
allow flow in any direction.
The geometric network is ideal for utilities and network dataset/network analyst for
transportation networks.
 The main difference is that geometric networks have the concept of "flow". i.e.
something moving along the network in a defined way.
 So you can perform tracing upstream/downstream. It does not have concepts such as
turn restrictions, turn delays, street name for directions, etc.

Analysis Application
Calculate the shortest path between two
points.
Various kinds of utility companies use this as a
method of inspecting the logical consistency of a
network and verifying connectivity between two
points.
Find all connected or disconnected
network elements.
Electric companies can see which part of the network
is disconnected and use that information to figure out
how to reconnect it.
Find loops or circuits in the network. An electrical short circuit can be discovered.
Determine flow direction of edges
when sources or sinks are set.
Managers or engineers can see the direction of flow
along edges, and ArcGIS can use the flow directions
to perform flow-specific network analyses.
Trace network elements upstream or
downstream from a point.
Water utilities can determine which valves to shut off
when a pipe bursts.
Calculate the shortest path upstream
from one point to another.
Environmental monitoring stations can hone in on a
source of pollution in streams.
Find all network elements upstream
from many points and determine which
elements are common to them all.
Electric utility companies can use the phone calls of
customers experiencing an outage to locate suspect
transformers or downed lines.

Geometric Networks
Edges
 An edge is a feature which has a length through which some commodity flows.
Edges are created from line feature classes in a feature dataset and correspond to
edge elements in a logical network.
 Examples of edges: water mains, electrical transmission lines, gas pipelines,
telephone lines, etc...
 Simple – Simple edges are always connected to exactly two junctions, one at
each end.
 An example of a simple edge would be a water lateral in a water network. The
water lateral connects at one end to a junction along the main distribution line
and, at the other end, to a service point junction (such as a tap or pump).
 Simple edges have no mid-span connectivity. If a new junction is snapped mid-
span on a simple edge, thereby establishing connectivity, then that simple edge is
physically split into two features.

Geometric Networks
Complex Edges
 Complex edges are always connected to at least two junctions at their endpoints
but can be connected to additional junctions along their length.
 An example of a complex edge would be a water main in a water network. The
main water distribution line is a single complex edge with multiple lateral lines
connected to junctions along its length. The water main is not split at the junction
where each lateral connects to the main.
 Complex edges have mid-span connectivity. If a new junction is snapped mid-
span on a complex edge, that complex edge remains a single feature. Snapping
the junction does cause the complex edge to be split logically—for example, if it
corresponded to one edge element in the logical network before the junction was
connected, it now corresponds to two edge elements.
 Complex edges correspond to one or more edge elements in the logical network.

Geometric Networks

Geometric Networks
Junctions
 A junction is a feature that allows two or more edges to connect and
facilitates the transfer of flow between edges. Junctions are created from
point feature classes in a feature dataset and correspond to junction
elements in the logical network.
 Examples of junctions: fuses, switches, service taps, valves, etc...
 User defined junctions ‐ Created based on point feature classes,
correspond to a single junction element in the logical network.
 Orphan junctions ‐ Will be inserted at the endpoint of any edge at which
a junction does not already exist, maintains network integrity
 If a point from a point feature class is not available to serve as a junction

Geometric Networks
Sources and Sinks
 Any of the features in the geometric dataset can take on the role of a source
(where a commodity flows from) or a sink (where a commodity terminates).
 These roles are used to define flow in the network.
 For example, the flow of electricity in an electrical network is from the power
generation station to the customers.
 the flow of water may be from a pump station to a customer or from customers
to a treatment plant

Network weights
 A weight can be used to represent the cost of traversing an element in the
logical network.
 Any number of attributes, for example lengths, capacity or slope.
 A network can have any number of weights associated with it. Each feature
class in the network may have some, all, or none of these weights associated
with its attributes.
 A network weight can be associated with only one attribute or with multiple
feature classes. For example, a weight called Diameter can be associated with
the attribute Diameter in the water main feature class and as well as with the
attribute Pipe_dia in the water lateral feature class.
 A network weight value of zero is reserved and is assigned to all orphan
junctions.
 Also, if a weight is not associated with any attributes of a feature class, then
the weight values for all network elements corresponding to that feature class
will be zero.

GISC 6382 UT‐Dallas Briggs 15
Network Analysis
• Network Traces
– 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

Tracing upstream and downstream
• Upstream trace
• Downstream trace

Finding Path
• Find the best path between two flags
– Upstream, downstream, connected
– From first flag to second flag
• Flags are placed on any feature

Finding common ancestor
• Piece of upstream network common to all
flags
– Which electric line is common to all house?

Finding connected features
• Finding features connected to a flag
• Commonly used for isolating features
– 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

Finding Indeterminate Flow
• Use the Find Loops analysis
No Cycle (switch open) Cycle (switch closed)

References
• http://desktop.arcgis.com/en/arcmap/10.3/manage‐
data/geometric‐networks/what‐are‐geometric‐networks‐.htm
data/geodatabases/exercise‐5‐building‐a‐geometric‐
network.htm
• http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicN
ame=What%20is%20a%20geometric%20network%3F
data/geometric‐networks/what‐are‐geometric‐networks‐.htm
• http://resources.esri.com/help/9.3/arcgisengine/dotnet/3b9a
f327‐e71d‐4c65‐b140‐ae19078355fa.htm

Network analysis in gis , part 5 geometric network

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