Rule-based location management

The concept of rule based event location management discusses the use and implementation of rule-based location management in the advanced linear referencing system (ALRS) to control what happens to events when the routes they are referenced to change.

What is event behavior?

Assets are usually located along a highway or other linear facility in a linear referencing system (LRS) using a location reference (for example, measure) that is relative to the overall length of the highway. Because location is based on the highway length, changes in the length have a direct impact on how the asset will be located and how it can be rendered in a map. The impact that changes to the highway system have on event locations is what we refer to as event behavior.

What is location?

In a highway system, location is the nominal placement of assets based on the length of the highway. Location is specific to a route definition and a system of measure. In the ALRS, that means each location is specified according to an LRS Network and the units that network is measured in. Location is expressed as a route and a measure value or a route, a referent, and an offset distance. A common way of thinking of location is that it is similar to a street address. The street name is analogous to the route identifier (ID), and the house number is analogous to the measure value. Sometimes, locations are expressed in terms of other locations. This is generally an offset distance from an asset that has already been located along the highway. For example, a crash might be described as 0.25 miles west of milepost 2. This is different from the milepost location of 2.25 because the distance between mileposts 2 and 3 may not be precisely one mile.

By describing assets and incidents in terms of location, you provide much more descriptive context than is possible with an x,y coordinate.

What is position?

In contrast to location, position is the exact x,y coordinate of an asset or incident regardless of its relative location along any particular highway. When rendering events in a map, ArcGIS converts locations to positions so they can be accurately rendered and properly overlaid with other geospatial information. By automatically converting location to position, the ALRS allows you to perform a wide variety of geospatial analysis using data that is traditionally considered nonspatial.

Location management rules

Location management is the process of prioritizing either location or position when the underlying LRS Network is modified. To control what happens to your events when the highway changes, you must establish a set of rules for each event layer. By telling the events what to do when the highway changes, we can establish priorities to preserve location, position, both, or neither. You have four options for setting location management rules.

Stay Put

The Stay Put rule preserves the position of the event. When the highway is modified, events retain their x,y coordinates. This means their measure values may be changed.

Example of event data with Stay Put behavior before a realignment

Example of event data with Stay Put behavior after a realignment

With Stay Put event behavior, events downstream of a realignment retain the position although their relative location along the route changes. Line events that intersect the realignment portion may be split into two or more events, so the portion not affected by the new alignment will retain its position. Events that are completely contained by the new alignment are retired.

Move

The Move rule preserves the location of the event. When the highway is modified, events retain their measure values. This means x,y coordinates may be changed.

Example of event data with Move behavior before a realignment

Example of event data with Move behavior after a realignment

Retire

Retire event behavior preserves both position and location. When you modify a route, the system flags the event as retired by changing its ToDate value. The event's measure does not change, but the event will no longer be displayed in the current alignment of the highway. If you want to see the event, you must set the event layer's temporal view date (TVD) to a date and time prior to the new alignment. You can set the TVD by opening the event layer's Layer Properties dialog box and clicking the ALRS tab.

Example of event data with Retire behavior before a realignment

Snap

Snap event behavior preserves the proportional location of an event by snapping the event to a new route or to the new alignment of the existing route. When you modify a highway, it is likely that events will fall within or extend into the alignment section that is to be retired. Since that portion of the highway no longer exists, these events have nowhere to go. As described earlier in this section, Stay Put behavior causes the portion that falls within the new alignment to be retired, and Move behavior causes it to appear on the new alignment as if the change had never taken place. In other words, Stay Put causes portions of the event to disappear, and Move causes the whole event to shift along the route.

In some cases neither behavior is desirable. It may be more desirable to have an event located one-fifth of the way along the original alignment to also be located one-fifth of the way along the new alignment. Suppose, for example, you were to realign a route between mile 10 and mile 15, adding an additional 15 miles to the route with the new alignment. Suppose, also, that you had an event at mile 11, which is 20 percent of the way along the original route alignment from mile 10 to mile 15. When you add 15 miles to the route at mile 10, the new alignment portion runs from mile 10 to mile 30. The event, which started 20 percent of the way along the original alignment, must now find itself 20 percent of the way along the new alignment. Since the difference between 10 and 30 is 20 miles, and 20 percent of 20 is 4 miles, the event's measure value would change from 11 to 14 (mile 10 plus 4 miles).

Example of event data with Snap behavior before a realignment

Snap behavior is particularly useful when the route being realigned overlaps with another route. In these cases you may want the event to snap to the route that is not being aligned rather than snapping to the new alignment.

Configuring location management rules

Event behavior is configured when you register events with the ALRS. You can also configure event behavior at any time by opening the event layer's properties. During the process of registering events through the ALRS Event Setup wizard, you can set event behavior rules for each type of activity applied to the highway. Event behavior rules do not apply to reference offset events.

How are location management rules impacted by workflow?

Each activity has a different impact on events, depending on where the event is in relation to the edit and what type of edit is being performed. Since each event behavior preserves specific information about the event, the relationship between location and activity can get somewhat complex. The following table explains what happens for each behavior rule when a particular edit activity is performed on a route.

Note:

All events that lie within the section of a route that does not have its calibration affected (that is, a net result in measure change) through the edit process, will remain unchanged.

Move Behavior

Activity	Event Upstream	Event Within Edit	Event Downstream
Extend Route	No Action	No Action	No Action
Recalibrate Route	No Action	No Action	No Action
Realign Route	No Action	No Action	No Action
Realign Overlapping Route	No Action	No Action	No Action
Retire Route	No Action	No Action	No Action
Reassign Route	No Action	No Action	No Action

Stay Put Behavior

Activity	Event Upstream	Event Within Edit	Event Downstream
Extend Route	No Action	No Action	M-value adjusted to retain x,y
Recalibrate Route	M-value adjusted to retain x,y	M-value adjusted to retain x,y	M-value adjusted to retain x,y
Realign Route	Behavior for recalibrate to first calibration point prior to edit	Retire events; line events crossing realignment portion will be split and original event retired	M-value adjusted to retain x,y
Realign Overlapping Route	Behavior for recalibrate to first point prior to edit	Retire event; line events crossing realignment portion will be split and original event retired	M-value adjusted to retain x,y
Retire Route	Behavior for recalibrate to first calibration point prior to edit	Retire event; line events crossing realignment portion will be split and original event retired	Behavior for recalibrate
Reassign Route	Behavior for recalibrate to first calibration point prior to edit	M and route reference adjusted for new assigned route; line events crossing reassigned portion will be split	Behavior for recalibrate

Retire Behavior

Activity	Event Upstream	Event Within Edit	Event Downstream
Extend Route	No Action	Retire event	Retire event
Recalibrate Route	Retire event	Retire event	Retire event
Realign Route	Behavior for recalibrate to first calibration point prior to edit	Retire event; line events will not be split	Behavior for recalibrate
Realign Overlapping Route	Behavior for recalibrate to first calibration point prior to edit	Retire event; line events will not be split	Behavior for recalibrate
Retire Route	Behavior for recalibrate to first calibration point prior to edit	Retire event; line events will not be split	Behavior for recalibrate
Reassign Route	Behavior for recalibrate to first calibration point prior to edit	Retire event; line events will not be split	Behavior for recalibrate

Snap Behavior

Activity	Event Upstream	Event Within Edit	Event Downstream
Extend Route	No Action	No Action	M-value adjusted to retain x,y
Recalibrate Route	Modify x,y, m, and/or route reference to maintain proportional location	Modify x,y, m, and/or route reference to maintain proportional location	Modify x,y, m, and/or route reference to maintain proportional location
Realign Route	Behavior for recalibrate to first calibration point prior to edit	Modify x,y, and/or m to maintain proportional location	Modify x,y, and/or m to maintain proportional location
Realign Overlapping Route	Behavior for recalibrate to first calibration point prior to edit	Modify x,y, m, and/or route reference to maintain proportional location	Modify x,y, m, and/or route reference to maintain proportional location
Retire Route	Behavior for recalibrate to first calibration point prior to edit	Retire event; line events crossing realign portion will be split	Behavior for recalibrate
Reassign Route	Behavior for recalibrate to first calibration point prior to edit	Modify x,y, m, and/or route reference to maintain proportional location; line events crossing reassign portion will be split	Behavior for recalibrate