The linear referencing system (LRS) is a collection of feature classes and tables that allow the storage and editing of calibrated routes.
The LRS supports the use of a single polyline feature class, known as a centerline, to store the geometry for multiple routes. Centerline geometry, along with route definitions, are stored in a network feature class.
A many-to-many relationship exists between the routes in the network and centerlines providing the geometry. This means that routes are typically composed of multiple centerline features, and centerline features can participate in multiple routes in multiple networks.
In addition to geometry, routes must also have measures. The LRS uses route measures so that event layers appear 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 LRS 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.
The LRS is comprised of the following feature classes and tables:
- Centerline—The polyline feature class that stores route geometry.
- Centerline Sequence—The cross-reference table that manages the relationship between centerlines and routes.
- Calibration Point—The point feature class that stores route measure values.
- Redline—The polyline feature class that stores markup features for communicating LRS changes.
Centerline feature class
The centerline feature class provides a single source of geometry for all of the LRS Networks you build in an LRS.
Every feature in the centerline feature class represents a single unit of the highway. These can be used to represent a one-to-one relationship with routes or be combined to form larger routes.
The LRS requires that the centerline feature class have a centerline ID field.
Field | Data type | Length | IsNullable | Description |
---|---|---|---|---|
Centerline ID | GUID | Yes | Unique ID for the centerline geometry |
Centerline sequence table
The many-to-many relationship between routes and centerlines is maintained through a cross-reference table known as the centerline sequence table. Since route IDs are not unique in the LRS, the centerline sequence table also contains a reference to the network ID field of the LRS Network. The combination of the network ID and route ID creates a way of uniquely identifying each route in the LRS. The use of the network ID helps differentiate between LRMs, as route IDs may not be unique across networks.
One centerline feature can participate in many routes, and a route can be comprised of more than one centerline. The centerline sequence table must have at least one record for each centerline-network combination.
The minimum fields for the centerline sequence table are as follows:
Field | Data type | Length | IsNullable | Description |
---|---|---|---|---|
Centerline ID | GUID | Yes | The unique ID for the centerline geometry. | |
FromDate | Date | 8 | Yes | The date that the portion of the centerline becomes active. |
ToDate | Date | 8 | Yes | The date that the portion of the centerline is retired. |
RouteId | String | Yes | The unique ID for the route. | |
NetworkId | Short Integer | 5 | Yes | The unique ID for the LRS network in which each route participates. |
Calibration point feature class
Route measures are assigned to routes in the network using the calibration point feature class. Routes are calibrated by calculating an interpolated distance between any two calibration points along the route. Calibration points are specific to an LRS Network and make up the measure component of the LRM. Calibration point rules are as follows:
- There is only one calibration point feature class for all LRS networks registered with the LRS.
- A minimum of two calibration points is required for each route.
- Calibration points should be monotonic, meaning strictly increasing or decreasing in measure along a route. Nonmonotonic routes will calibrate but can result in undefined event locations and event behavior.
- Add a calibration point to a particular location to maintain a specific measure value.
The minimum fields for the calibration point feature class are as follows:
Field | Data type | Length | IsNullable | Description |
---|---|---|---|---|
Measure | Double | 8 | Yes | The measure value stored for routes in an LRS Network. |
From Date | Date | 8 | Yes | The date that the calibration point becomes active. |
To Date | Date | 8 | Yes | The date that the calibration point is retired. |
Route ID | String | 255 | No | The unique ID for the route. |
Network ID | Short Integer | 5 | Yes | The unique ID for the LRS Network. |
Tools are provided to help generate and update calibration points, as well as to detect nonmonotonic calibration on your routes.
Redline feature class
The redline feature class contains the basic information required to perform many of the route editing functions available in ArcGIS Roads and Highways. This markup feature is a placeholder for a future route editing operation used to alert an LRS Editor to necessary changes.
The minimum fields for the redline feature class are as follows:
Field | Data type | Length | IsNullable | Description |
---|---|---|---|---|
From Measure | Double | 8 | Yes | The starting measure of the alignment change. |
To Measure | Double | 8 | Yes | The ending measure of the alignment change. |
Route ID | String | 255 | No | The unique ID for the target route. |
Route Name | String | 38 | Yes | The name for the route. |
Effective Date | Date | 8 | Yes | The date that the route change becomes effective. This date is applied to events affected by the change if the effective date applies. |
Activity Type | Short Integer | 5 | Yes | The edit activity that should be made, such as Extend Route. |
Network ID | Short Integer | 5 | Yes | The unique ID of the LRS Network. |
Redline features can be entered as specifically or generally. It is expected that a GIS analyst will verify the redline feature and ensure that accurate geometry is entered into the database. A roughly sketched redline indicates that a change to the LRS is required and provides its general location.
Network feature class
The network feature class contains the route features used in the LRS. These routes have attributes, geometry from the centerline feature class, and calibration from the calibration point feature class.
Combined, these elements constitute a route in the LRM that can be used to locate events on that route. Each route should have a unique route identifier, called a route ID. The route ID can be a single field or a concatenation of multiple fields. If the network will use a concatenated route ID, all of the fields that comprise the route ID must be present in the network feature class, in addition to the RouteId field.
The route ID field data should be consistent throughout networks, events, calibration point feature classes, and the centerline sequence feature table.
The minimum fields for the network feature class are as follows:
Field | Data type | Length | IsNullable | Description |
---|---|---|---|---|
From Date | Date | 8 | Yes | The date that the portion of centerline becomes an active part of the route. |
To Date | Date | 8 | Yes | The date that the portion of centerline becomes a retired part of the route. |
Route ID | String | 255 | No | The unique ID for the route. |
The following fields must be configured if using a multifield route ID composed of several other fields in the network feature class:
Field | Data type | Length | IsNullable | Description |
---|---|---|---|---|
Fields that comprise the routeID field. | String, Short Integer, and Long Integer | Less than or equal to the RouteId field length | Yes | The fields that comprise the concatenated route ID for the network. Each field should be modeled separately in the network feature class. |