The ARNOLD requirements pose many challenges, one of which is how to identify or reference local roads where mileposts do not exist, or for which driven mileage is not recorded. As a result, the popular Milepoint or Reference Post LRMs are no longer applicable.
Usher in the most flexible LRM – Reference Point w/ Offset. This LRM treats any features or landmarks such as cross streets, rivers, railways and bridges – even non-physical features like state/county boundaries – as reference points.
There are important advantages to using the Reference Point LRM. First, the “plain-English” location description can be easily understood by humans. Second, as long as stable intersecting features or landmarks are chosen as reference points, route changes such as extensions or realignments will not require cascading measure updates for events on the routes.
In fact, with the Reference Point LRM, route measures are no longer carried in asset or event tables in the database. But what if we want to map event/assets via dynamic segmentation? This is where the Route Reference table (also known as “Intersection” table or “Extended Intersection” table) comes into play. It serves as a look-up table for measures, as it contains measures identifying the location of intersecting features and landmarks along routes.
Using a fictitious section of route Oak Rd illustrated below, the corresponding Route Reference table is shown in Table 1.
|Oak Rd||0||Node Rail Route||Begin||1|
|Oak Rd||0.5||Route||Maple Ln||Left||500|
|Oak Rd||0.5||Route||A St||Cross||500|
|Oak Rd||1.0||Route||B St||Right||1000|
|Oak Rd||1.8||Rail||Rail Tracks||Cross||1800|
|Oak Rd||2.2||Route||D St||Cross||2200|
|Oak Rd||3.0||Boundary||Co. Boundary||Cross||3000|
A basic Route Reference table should at least include route break points, intersecting routes/features and their intersection configurations. Additional attributes such as address values at intersections, and the geometric angles at which the intersecting features cross the route, can also be desirable.
A Route Reference table is derived from GIS layers that are related, such as road centerline, route and other feature layers such as rail networks, streams and rivers, and various boundaries, etc. Because of its dependencies on other layers, each time there is a change in the source or contributing layers, the Route Reference table will need to be regenerated.
LinearBench offers an off-the-shelf, Route Reference table generation solution that is feature-rich and efficient.