Barriers are used in traces to mark locations where a trace should stop.
There are two types of barriers in a trace network:
- Feature barriers—Created on a map using the Trace Locations pane or by specifying another feature class to serve as a barrier.
- Dynamic barriers—Network features that meet criteria defined by a condition or function barrier.
Feature barriers are created by specifying the network features to serve as barriers when configuring a trace. Dynamic barriers allow you to use information about your network features to create barriers.
Feature barriers
Barriers can be created through the Barriers tab in the Trace Locations pane or by specifying an existing feature class in the Barriers parameter of the Trace tool.
Feature (or physical) barriers are optional during tracing events. To include them, you use a tool to set areas in your network as barriers for a trace.
Only network features can be used to place barriers with the Trace Locations pane. When a network feature is selected or added from a selection set, the following are true:
- For point features, a coincident point is created to denote the barrier for the trace.
- For lines, a barrier can be placed anywhere along the line feature.
When a barrier is established using the Trace Locations pane, a feature class named
TN_Temp_Barriers is created in the project's default
geodatabase. Successive feature barriers are appended to this class.
To remove all barriers from a map, click the Clear All button
.
When an existing feature class is used to supply barriers for the Trace tool, the source feature class must contain a FEATUREGLOBALID field similar to that found in the TN_Temp_Barriers feature class and contain a value for it to be applied to the corresponding network feature as a barrier.
In scenarios where this field is not populated, the specific feature is not used to place a barrier. This option is helpful when you want to maintain granularity over which features serve as barriers when coincident geometries exist. If the FEATUREGLOBALID field is not present in the schema of the feature class, the geometry of the input feature class is used to intersect the network feature geometry and place a barrier feature.
Keep the following information in mind when using existing feature classes as barriers:
- The TN_Temp_Barriers feature class is not used with this method.
- Selection sets on the input feature class are not honored.
- For polygons, barriers are placed along the boundary where network features intersect the polygon geometry.
Dynamic barriers
In addition to feature barriers, dynamic (or configurable) barriers can be set on network attributes or function conditions. During a trace operation, dynamic barriers can be modified.
Two types of dynamic barriers are used during a trace: Condition Barriers and Function Barriers. Both types are considered during a trace.
Note:
When using the Include Barrier Features configuration option for barriers placed along an edge, the trace results include the entire feature. The Result Types option Aggregate Geometry can be used to return partial feature results. When a barrier is placed midspan on an edge, trace results stop at the barrier and return partial feature geometry of the edge feature.
Condition barriers
A condition barrier is an expression based on network attributes, for example, to stop at all water bodies that have indeterminate flow in a hydrologic network. When a feature meets the condition set in the expression, the trace operation does not continue to the next feature.
More than one condition barrier can be implemented using the Combine Using parameter (AND or OR).
Function barriers
Function barriers define the extent of a trace based on whether a function condition has been satisfied. Function barriers can be used to do such things as restrict how far a trace travels from the starting point, or set a maximum value to stop a trace. For example, the length of each line traveled is added to the total distance traveled. The Add function could be used to set a maximum value, and when the total length traveled reaches the value specified, the trace stops.
Networks often have paths that fork into multiple paths. At times, you may want to consider all forked paths together (global) and at other times consider them as separate paths from one another (local). Using the example of distance along paths in a trail network, if the starting point is placed at a fork with three paths, and the trace is set to trace 3 kilometers down the trails using global values, the trace will travel 1 kilometer down each of the three forked paths. When you enable the Use Local Values option, the trace will travel 3 miles down each of the three forked paths.
More than one barrier type can be used at once. Combining barriers allows you to control a group of diverse, precise types of barriers. Suppose you want to run a trace and have it stop at any disabled line segment, but you don't want the trace to travel more than 500 meters beyond the starting point. To accomplish this, you'd use a condition barrier to control the network attribute value that denotes a disabled line that stops a trace, and you'd use a function barrier to calculate the length of the line you travel and set a limit of 500 meters.
Note:
When executing a trace using a function barrier with the Use Local Values option selected, only one starting point is allowed.
To learn more about setting barriers, see Configure a trace.