Defining relationships in the ALRS

The advanced linear referencing system (ALRS) supports the use of a single polyline feature class, known as centerlines, to store the geometry for multiple highway definitions, known as routes. The route definitions are stored in a route table, which has a many-to-many relationship to centerlines. This means that routes are typically made up of multiple centerline features and centerline features can participate in multiple routes. The many-to-many relationship between routes and centerlines is maintained through a cross-reference table known as the centerline sequence table. Centerline sequence contains a reference to each centerline indicating which routes the centerline participates in. Because route IDs are not unique in the ALRS, the centerline sequence table also contains a reference to the LRS Network. The combination of NetworkId and RouteId creates a way of uniquely identifying each route in the ALRS.

In addition to geometry, routes must also have measures. Measures on routes are what the ALRS uses to display event layers in their correct locations on a map. Measures are added to routes through a process known as calibration. To explicitly control how routes are calibrated, the ALRS uses a calibration point feature class. Calibration points are point features that store measure values, route references, and network IDs. The combination of these three items constitutes a linear referencing method (LRM). LRMs are created by applying calibration points to routes to create an LRS Network.

Before LRS Networks can be created, however, the relationships between the ALRS data elements must be established. This is done when you create a new ALRS using the Advanced Linear Reference System Setup wizard. You should organize your data so that it will be easier to run the ALRS wizard and configure your route relationships.

Steps:

1. Identify the field in the centerline feature class that will act as a unique identifier.
   • ObjectID—If you don't already have a field defined, use ObjectId.
   • User-defined roadway ID—If you already maintain a field to uniquely identify centerlines or control sections and this is the first time creating an ALRS, use this.
   • RoadwayIdGuid—If you have already created an ALRS using this set of centerlines, the RoadwayIdGuid has already been created and should be used from this point on.
2. Create a field in the centerline sequence table to store the RoadwayId.
   • If the RoadwayIdGuid has not yet been created, this will be the RoadwayId or ObjectID from the centerline feature class.
   • If the RoadwayIdGuid has already been created, this will be the RoadwayIdGuid from the centerline feature class. The first time you create an ALRS, the system will append RoadwayIdGuid to the centerline sequence and populate it with the correct values.
3. Create a field in the centerline sequence table to store the route identifier. The RouteId field may not be based on any single field within the route table since Roads and Highways supports the creation of route IDs by combining fields in the route table.
4. Create a field in the centerline sequence table to store the network identifier. NetworkId should be an integer field that points to the dLRSNetworks domain in the geodatabase. If dLRSNetworks does not already exist, it will be created for you when you create your first ALRS.
5. Construct your centerline sequence. This is done by appending route information to centerlines. If you already have routes in an ArcGIS format, you can do this using geoprocessing tools. You can find sample geoprocessing tools for creating centerline sequence on the Roads and Highways Resource Center at http://resources.arcgis.com/content/roads-highways/data-management.
6. Populate NetworkIds in the centerline sequence table. Your first network will have a NetworkId value of 1.

   Until you have built your first ALRS and started adding networks, the dLRSNetworks domain will not be populated. Instead of populating the domain in advance, you must keep track of the integer value you assign to each network in centerline sequence and ensure that you create your networks in the same order. The easiest way to ensure the same network order for centerline sequence, calibration point, and LRS Network is to work with one network at a time. Once you have built your first LRS Network, you can go back and populate NetworkIds in the centerline sequence table and the calibration point feature class for the next network.

7. Create a field in the calibration point feature class to store the route identifier.
8. Create a field in the calibration point feature class to store the network identifier.
9. Use the Generate Calibration Points with no ALRS geoprocessing tool to create calibration points from existing route features.
10. Create the ALRS using the Advanced Linear Reference System Setup wizard.
11. Add your first LRS Network to your ALRS by opening the ALRS Properties dialog box, selecting the Networks tab, then clicking Add. See Creating LRS Networks to learn more about adding LRS Networks.
12. Repeat steps 5, 6, and 9 for each network you want to create.