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Trace a utility network

On the ArcGIS platform, utility networks offer a framework for modeling utility systems, such as electric, gas, water, storm water, wastewater, and telecommunications. Each utility network demonstrates how features are connected and how dynamic devices are configured. This topic describes how to build ArcGIS Runtime apps that can trace the flow of resources, such as gas, water, and electricity, through its network. For an overview of utility networks, see ArcGIS Pro's help topic What is a utility network?.

You can explore how a network is affected by real-world events such as storms, outages, or equipment failure, by asking questions like,

  • How is your network connected?
  • How does electricity/gas/water reach your house?
  • If a device is disabled, what section of the network will be out of power?

To help answer these questions, ArcGIS Runtime supports the following utility trace types:

  • Upstream—In a source-based network (gas or electric), an upstream trace is against the flow and toward the source, such as a circuit breaker or generator (subnetwork controller). In a sink-based network (sewer or storm water), an upstream trace is against the flow and away from the sink such as a sewage treatment (subnetwork controller). For more information, see ArcGIS Pro's help discussion on upstream traces
  • Downstream—In a source-based network, a downstream trace is with the flow and away from the source, such as a circuit breaker or generator. In a sink-based network, a downstream trace is with the flow and toward the sink. For more information, see ArcGIS Pro's help discussion on downstream traces.
  • Subnetwork—A trace that discovers all features participating in a subnetwork. This trace type is useful for validating whether subnetworks, such as circuits or zones, are defined or edited appropriately. The trace begins at one or more starting points and spans outward along connected features to find subnetwork controllers that are traversable. A subnetwork trace stops when it encounters a barrier, when it encounters a feature that is not traversable, or when there are no more connected features. For more information see ArcGIS Pro's help discussion on subnetwork trace.
  • Isolation—A trace used to determine the minimum set of operable assets (point and line features) required to stop a network's resource from traveling/flowing, effectively isolating an area of the network. For instance, when a leak occurs on a water network, particular valves must be closed to eliminate water flow at the leak location. This prevents damage and allows field crews to safely start the repair process. For more information, see ArcGIS Pro's help discussion on locating isolating features.
  • Connected—A trace that begins at one or more starting points and spans outward radially along connected features. A trace stops when a barrier is encountered or there are no more connected features. Can be used for validating newly edited features to ensure they are connected as expected. For more information, see ArcGIS Pro's help discussions on connectivity and finding connected features.

To trace a utility network you need to:

  1. Use ArcGIS Pro to create a utility network
  2. In ArcGIS Runtime, access the utility network
  3. Define the trace parameters
    1. Decide which trace type to perform
    2. Define the starting and barrier locations
    3. Specify the trace configuration
  4. Run the trace
  5. Examine the results

Access the utility network

Utility networks are implemented in service-based geodatabases as network controller datasets. These datasets contain a network's service feature tables along with the network's domains, sources, tiers, assets, terminals, rules and associations. This utility network is accessible via these service feature tables stored in a single feature service.

You can display and share a complete utility network with a user via a web map if the map includes one feature layer for every network source.

Diagram of objects loaded when loading a utility network with a map with layers for all network sources.

To display and share the utility network, create a utility network object from a feature service URL and a web map that contains all the layers that participate in the utility network.

var utilityNetwork = AGSUtilityNetwork(url: featureServiceURL, map: map)

Note:

The feature service provides access to the topological network in the utility network. So, you could provide a map that contains just a subset of the feature layers, for a specific workflow. Any tracing would be performed using the full topological network provided by the feature service. If you need to add additional utility network layers you can create them from the individual network sources, as required.

You can also access a utility network and run a trace completely without a map. Just provide the feature service URL when you create the utility network. If needed, you can create a completely new map by creating feature layers from the network sources.

var utilityNetwork = AGSUtilityNetwork(url: featureServiceURL)

Note:

ArcGIS Runtime supports Utility Network version 2 and later that is provided from ArcGIS Pro 2.2 onwards. For details see utility network upgrade history.

Load the utility network

The utility network follows the loadable pattern for asynchronous resources. Loading the utility network loads the entire utility network schema (information about the datasets that participate in the network). Once loaded, your app can navigate this network schema to discover the domain networks it contains and any further details about the network.

utilityNetwork.load { [weak self] error in
 if let error = error {
  print("Loading Utility Network Failed")
  return
 }

 //continue with the utility network
 print("The Utility Network schema version is \(self?.utilityNetwork.definition.schemaVersion)")

}

Define the trace parameters

Trace parameters define how the trace analysis proceeds across the utility network. These are the essential trace parameters:

  1. Trace type
  2. Start and barrier locations
  3. Trace configuration

Trace type

ArcGIS Runtime supports the trace types described above (upstream, downstream, and so on).

Use the utility trace type to create the parameters

Create a set of AGSUtilityTraceParameters by providing a AGSUtilityTraceType of upstream, downstream, isolationsubnetwork, or connected, along with a collection of starting locations (if known at this stage).

var utilityTraceParameters = AGSUtilityTraceParameters(traceType: .upstream, startingLocations: [])

Start and barrier locations

Each trace requires one or more locations from which to initiate the trace. Optionally, you can also include barrier locations. Starting and barrier locations are defined using instances of UtilityElement which are added to the trace configuration's starting locations and barriers collection respectively.

You can create a starting location using steps like the following:

  1. Create a UtilityElement using a feature.

    guard let utilityElement = utilityNetwork.createElement(with: feature, terminal: nil) else {return}

    1. If the feature represents a line, you can optionally specify a location along the line to use as the starting location. This value is expressed as a percentage of the length of the line, beginning from the line's from point. Set the fractionAlongEdge value to define the location of the point along the line.

      // Determine how far the starting point is located along a line
        let geometry = feature.geometry
        let line = AGSGeometryEngine.geometryByRemovingZ(from: geometry) as? AGSPolyline 
        utilityElement.fractionAlongEdge = AGSGeometryEngine.fraction(alongLine: line, to: mapPoint, tolerance: -1)

    2. If the feature represents a device with terminals, you must specify which terminal you want to use as the starting point.

      guard let terminals = utilityElement.assetType.terminalConfiguration?.terminals else {return}
       let terminal = terminals[0]
                  
       utilityElement.terminal = terminal

  2. Add the utility element to the utility trace parameters’ startingLocations collection.

    self.utilityTraceParameters.startingLocations.append(utilityElement)

  3. If you need to add a barrier, complete step 1 above then add the utility element representing a barrier to the utility trace parameters’ barriers collection.

Trace configuration

If you don't want to use the trace configuration as created in ArcGIS Pro, you can either modify it or you can override it with settings you specify with ArcGIS Runtime. A trace configuration is set on the AGSUtilityTraceParameters.

These settings allow you to do things like:

  • Stop the trace at protective devices if they are open. For example, the flow of electricity in a network will be stopped if a fuse is open.
  • Control the types of features traced. For example, trace only pipes with a diameter greater than six inches.

Each trace configuration manages basic properties such as:

  • Include barriers in trace results
  • Include containers in trace results
  • Include content in trace results
  • Include structures in trace results
  • Add filter barriers (required for isolation traces)
  • Ignore barriers if they are the starting points
  • Domain network
  • Source tier
For more advanced properties, such as traversability, propagators, and target tiers see the advanced trace configuration section.

When a utility network administrator creates a new tier in ArcGIS Pro, a subnetwork trace configuration is created and populated as described in Configure a trace.

You can choose if your app uses the trace configuration as defined by an administrator, a modified version of the configuration, or your own trace configuration.

Use a trace configuration defined in a utility network tier

To obtain the trace configuration from a utility network tier, you need to know the name of the domain network and the tier.

  1. Obtain the utility network definition from the utility network.
  2. Get the domain network from the utility network definition.
  3. Obtain the tier from the domain network.
  4. Pass the tier's trace configuration to the utility trace parameters.
  5. Modify any of these properties as required.

    let utilityNetwork = AGSUtilityNetwork(url: theFeatureServiceURL)
            
    utilityNetwork.load {[weak self] (error) in
    
     //get the network domain called "ElectricDistribution"
     guard let utilityNetworkDomain = utilityNetwork.definition.domainNetwork(withDomainNetworkName: "ElectricDistribution") else {
      print("Utility Network Domain not found")  
      return
     }
        
     //get the tier called "Medium Voltage Radial"          
     guard let utilityTier = utilityNetworkDomain.tier(withName: "Medium Voltage Radial") else {
      print("Utility Tier not found")          
      return
     }
     
     //get the tier's traceconfiguration
     let traceConfiguration = utilityTier.traceConfiguration
    
     self?.utilityTraceParameters.traceConfiguration = traceConfiguration
    }

Create your own trace configuration

You can create your own trace configuration.

  1. Create a utility trace configuration.
  2. If you are running an upstream, downstream, or subnetwork trace then you must set the domain network as follows:
    1. Obtain the domain network from the utility network definition.
    2. Pass the domain network to the utility trace configuration.
  3. Modify any of the other properties, as required
  4. Pass the utility trace configuration to the utility trace parameters.

    let utilityNetwork = AGSUtilityNetwork(url: theURL)
    
    utilityNetwork.load { (error) in
        
     if let error = error { print(error.localizedDescription)
      return
     }      
     
     //create the utility trace configuration
     let traceConfiguration = AGSUtilityTraceConfiguration()
    
     //set the network domain called "ElectricDistribution" on the utility trace configuration
     guard let utilityNetworkDomain = utilityNetwork.definition.domainNetwork(withDomainNetworkName: "ElectricDistribution") else {
      return
     }            
     traceConfiguration.domainNetwork = utilityNetwork.definition.domainNetwork(withDomainNetworkName: "ElectricDistribution")
            
     //modify any other parameters, as required
       
     self?.utilityTraceParameters.traceConfiguration = traceConfiguration         
    }

Execute the trace

Run the trace by calling the trace method on the utility network object. Use the utility trace parameters defined in the previous section. In this release of ArcGIS Runtime, all utility trace results are returned as utility element trace results.

// Perform the trace
utilityNetwork.trace(with: self.utilityTraceParameters) { [weak self] (utilityTraceResult, error) in
 if let error = error {
  print(error)
  return
 }
            
 //process the trace result
 ...

}

If the trace fails you can examine why. For example, failure could be due to dirty areas in the network topology.

Examine the results

To display the results of this trace on a map, or to analyze them further, you need to obtain the corresponding features for these elements as described in the following steps.

  1. Filter the utility element trace results to find those that are part of the map, and group them by network source name.
  2. For every group (network source with utility elements), make sure there is a layer in the map for the features. Next find the features corresponding to the utility elements.

    guard let elementTraceResult = traceResult.first as? AGSUtilityElementTraceResult,
      !elementTraceResult.elements.isEmpty 
      else {
      print("Trace returns no results")
      return
    }
    
    let groupedElements = Dictionary(grouping: elementTraceResult.elements, by: { $0.networkSource.name })
    
    for (networkSourceName, elements) in groupedElements {
     
     // ensure that the features' layer exists in the map 
     guard let layer = self.map.operationalLayers.first(
      where: { ($0 as? AGSFeatureLayer)?.featureTable?.tableName == networkSourceName }) as? AGSFeatureLayer 
      else { continue }
    
     // get the features that correspond to the elements
     self.utilityNetwork.features(for: elements, completion: { [layer, networkSourceName] (features, error) in
    
     guard let features = features else { return }
    
     })
    }

  3. Select the features that correspond to the trace result or process as required.

    // Select features to highlight result
    layer.select(features)

Advanced trace configuration

Traversability

As you trace a topological network you can examine a number of constraints or conditions that could stop the trace. For example, you can stop tracing the network if:

  • A water valve is closed
  • An electric switch is open
  • A distance of 1000 m is reached
  • The gas pipe is made of plastic
The ability for a trace to traverse the topological network is defined by the traversability property on the AGSUtilityTraceConfiguration class. You can set conditions or constraints to this trace using barriers and function barrier properties.

Barriers and function barriers used as traversability constraints are defined using a condition, such as a valve being closed, encountering a particular material type, reaching a specified threshold along the trace, and so on. This contrasts with barriers that may be defined with trace parameters, which are defined using utility network elements, often selected interactively by the user.

Barriers

Set up a trace barrier by comparing the value of an asset's attribute or by examining the existence of a UtilityCategory. You can compare them individually or combine them with boolean And / Or operations into complex filters.

  • Use the AGSUtilityNetworkAttributeComparison class to compare an element's network attribute. For example, compare an attribute value to:
    • A specific value (for example, "DeviceStatus not equal to 4"), and/or
    • Another network attribute on the same element (for example, "SeasonalDeviceStatus" <> "NormalDeviceStatus")

    guard let lifecycleNetworkAttribute = utilityNetwork.definition.networkAttribute(withName: "Lifecycle") else {return}
                
    // Create a network attribute comparison that stops traversal if Lifecycle <> 4)
    let inDesignNetworkAttributeComparison = AGSUtilityNetworkAttributeComparison(networkAttribute: lifecycleNetworkAttribute, comparisonOperator: .notEqual, value: 4)
                
    // Create a network attribute comparison to stop traversal if Lifecycle <> 8
    let inServiceNetworkAttributeComparison = AGSUtilityNetworkAttributeComparison(networkAttribute: lifecycleNetworkAttribute, comparisonOperator: .notEqual, value: 8)
                
    // Combine these two comparisons together with "And"
    let lifecycleFilter = AGSUtilityTraceAndCondition(leftExpression: inDesignNetworkAttributeComparison, rightExpression: inServiceNetworkAttributeComparison)
                
    // Final condition stops traversal if Lifecycle <> 4 and Lifecycle <> 8
    traceConfiguration.traversability?.barriers = lifecycleFilter

  • Check a utility element's asset type to see whether that asset type (and thus the element) is included in a specific category using the AGSUtilityCategoryComparison class.

Function barriers

You can create a function barrier to terminate network traversal whenever a function expression evaluates to true. The function barrier compares the current results of a function and a given value. For example, you can use the function barrier to stop traversal after the trace traverses 1000 m along the network.

//create a network attribute object for the Shape length network attribute from the utility network definition
guard let shapeLengthNetworkAttribute = utilityNetwork.definition.networkAttribute(withName: "Shape length") else {return}
            
//create a function that adds up shape length
let lengthFunction = AGSUtilityTraceFunction(functionType: .add, networkAttribute: shapeLengthNetworkAttribute)
            
//create a function barrier that stops traversal after 1000 meters
let distanceBarrier = AGSUtilityTraceFunctionBarrier(traceFunction: lengthFunction, comparisonOperator: .greaterThan, value: 1000.0)
            
//set this function barrier
traceConfiguration.traversability?.functionBarriers.append(distanceBarrier)

For more information see traversability.

Note:

The AGSUtilityTraversabilityScope property determines whether these conditions are evaluated on edges, junctions, or both.

Trace filters

Filters are a mechanism to stop tracing when returning results. They do not stop traversability to the controller.

A trace filter and traversability both have properties for defining barriers, function barriers, and scope. These properties work the same way in both classes. What makes them different is when they get applied and how they affect the trace.

While both traversability and trace filter can terminate a trace, they have slightly different use cases. In upstream and downstream traces, traversability is considered first because it determines the subnetwork controller and the flow direction of tracing. If the controller's type is source-based, the flow direction is away from the identified subnetwork controller. If the controller's type is sink-based, the flow direction is toward the controller. Once the starting location, subnetwork controller, and flow direction are all established, the features that are traversable are then evaluated against the trace filter criteria.

If you want a trace to find the next upstream protective device in an electrical network, for example, you would create a AGSUtilityCategoryComparison where 'Protective Device' category exists. If you set this barrier on traversability, the trace will fail. It will be unable to find a subnetwork controller to determine which direction is upstream. You should use a trace filter instead.

Trace filter barriers can be used to configure isolation traces. An isolation trace allows you to isolate a portion of the network using filter barriers. An upstream trace configured to use isolation valves as filter barriers will determine the boundary of the isolation zone, from which you can determine which customers are affected (out of service).

Bitset network attributes

Bitset network attributes are only applicable to upstream and downstream trace types. They can be used to add special logic during a trace so the trace is more reflective of real world scenarios.

There are cases where traces need to be aware that a network attribute is a bitset that controls traversability. For example, you might have an electrical network in which phase is represented as a bitset network attribute (one bit per phase), and overhead electrical devices are represented with one device per phase. You could use a bitset network attribute to ensure the trace results include valid paths that are specified in the network attribute, not all paths.

Nearest neighbor

The nearest neighbor filter, AGSUtilityNearestNeighbor, allows you to return a specified number of features from the starting location of the trace. When assigned to a AGSUtilityTraceFilter, it will return a number of features of a certain type within a given distance.

A network attribute that represents travel cost is used to define the distance, which is typically shape length. Other attributes may be more useful depending on circumstances. For example, if you are searching for the "nearest" vault in an underground structure network, you may prefer a geographically distant vault that is connected via a duct bank rather than a closer one through a direct-buried trench (since excavating the trench is more costly). In this case a different attribute that represents the cost per segment should be used.

The type of features to be returned can be specified by utility category, asset type, or both. A valid AGSUtilityNearestNeighbor therefore, will have a cost network attribute, a count greater than 0, and at least one specified category or asset type.

Propagators

A propagator defines the propagation of a network attribute along a traversal and provides a filter to stop traversal. Propagators are only applicable to subnetwork-based traces (subnetwork, upstream, or downstream). One example is electric phase propagation, where open devices along the network will restrict some phases from continuing along the trace.

//get a network attribute object for the "Phases Normal" attribute from the utility network definition
guard let networkAttribute = utilityNetwork.definition.networkAttribute(withName: "Phases Normal") else {return}

//create a propagator to propagate the attribute using a Bitwise And function
let propagator = AGSUtilityPropagator(networkAttribute: networkAttribute, propagatorFunctionType: .bitwiseAnd, comparisonOperator: .includesAny, value: 7)

//assign the propagator to the trace configuration
traceConfiguration.propagators.append(propagator)

For more information see propagators.

Target tiers

All upstream and downstream traces can operate across the current tier (source tier). If you want your upstream or downstream trace to continue into another tier, you set the targetTier property on the AGSUtilityTraceConfiguration.

Tracing considerations

Dirty areas

All tracing operations rely on a topological index that is built from the utility network. If the network has been edited but the topology is out of date then it can contain dirty areas. For more information see ArcGIS Pro's discussion validate the network topology. If the topological network has dirty areas you can adopt a different approach depending on your app's purpose:

  • If the app must trace with the latest data (for example, an outage management app), an error should be returned to the user if it encounters a dirty area.
  • If the app can trace with a network that is out of sync with the feature (for example, a pole inspection app), then you should consider whether to set validateConsistency to false on the AGSUtilityTraceConfiguration. You can optionally display a warning to the user if a dirty area is encountered.

Get associated utility elements

Associations model the following types of relationships between two utility network elements:

AssociationDescriptionGeometry supported

Connectivity

Models the connectivity between two junctions that don't have geometric coincidence (are not in the same x, y and z location). A transformer may be connected to a fuse, for example.

Yes

Structural

attachment

Models equipment attached to structures. A transformer bank may be attached to a pole, for example.

Yes

Containment

Models assets that contain other assets. A vault may contain valves and pipes, for example.

No

An association is defined between two AGSUtilityElement objects. You can identify which AGSUtilityElements are associated with a given AGSUtilityElement using one of the associations methods on the AGSUtilityNetwork.

//get the elements associated with a single utility element (using containment)
utilityNetwork.associations(with: utilityElement, type: .containment) { (associations, error) in
 if let error = error {return}
 guard let associations = associations else {return}
                
  for association in associations {
   let fromElement = association.fromElement
   let toElement = association.toElement
  }
}

If the association represents a connectivity or structural attachment association, it may include a geometry value (polyline) representing the connection relationship between a from element and a to element. You can use the geometry to visualize the association as a graphic in the map.

If you want to find all the valid associations within a specific extent, call the associations method and provide an envelope that defines the specific extent.

Association graphics showing connectivity (red) and structural attachment (green) associations between utility elements

For more information see ArcGIS Pro's help topic Associations.