Iowa DOT’s Multi Level Linear Referencing System
February 23, 2009
Summary of the Federal Highway Administration’s Quarterly Webinar: Applications of Geospatial Technologies in Transportation
These notes provide a brief summary of the PowerPoint presentation discussed during the webinar. The focus of these notes is on the question-and-answer session that followed the PowerPoint presentation. The presentation is available upon request from the webinar speakers, Eric Abrams (email@example.com) and Steve Kadoph (firstname.lastname@example.org).
Approximately 80 participants attended the webinar.
Introduction to Presentation
Mark Sarmiento of the Federal Highway Administration's (FHWA) Office of Interstate and Border Planning thanked participants for joining the webinar. This webinar was the second in a quarterly series of webinars dealing with the application of geospatial information systems (GIS) and other geospatial technologies to transportation. This webinar focused on the multi-level linear referencing system (MLLRS) developed at Iowa DOT.
The American Association of State Highway and Transportation Officials' (AASHTO) Technology Implementation Group (TIG) has awarded Iowa a grant to promote its MLLRS based on the National Cooperative Highway Research Program (NCHRP) 20-27 model.
An LRS is a set of procedures and methods for specifying a location as a distance, or offset, along a linear feature, from a point with a known location. MLLRS represents objects as they occur in space and time.
The Iowa DOT reported several business reasons for implementing the LRS, including:
- Need to integrate a variety of business data, such as mile post referenced data and literal descriptions
- Need to improve spatial and temporal representation of data
To implement its LRS, Iowa DOT chose to use the NCHRP 20-27 model, which includes location referencing methods (LRMs). These LRMs are the most frequently used methods for location of business data. Multiple centerline representations are included in the model.
The benefit of the 20-27 model is that moving data from one location occurs through one central datum location rather than having multiple transformations occur simultaneously. The 20-27 model has mapping/routing capabilities and enables both spatial and temporal resolution.
Iowa DOT uses Oracle Spatial Data Option (SDO), a spatial indexing system, as the back-end software for its LRS. The Oracle SDO software represents objects in a network and performs various spatial analysis operations. Iowa extended the capabilities of Oracle SDO by building an Effective Date Lineage (EDL) system on top of the back-end software. EDL effectively aped temporal functionality to Oracle. Iowa DOT also built the Iowa DOT LRS extension (ILX) on top of Bentley LDMx software to meet the 20-27 model and DOT business rule requirements.
Iowa DOT uses commercial off-the-shelf (COTS) products (Oracle and GeoMedia Pro) as they have the ability to store data in a vendor-neutral environment and a database functionality to do spatial and database queries using a standard query language (SQL). COTS Oracle and GeoMedia Pro can also leverage existing feature creation functionality in a GIS. This can help to control costs during development.
In order to implement the 20-27 model, Iowa developed a maintenance tool that manages relationships to preserve all changes to the data. This tool propagates spatial accuracy changes to dependent features and manages all route sequencing as the network changes. Users can control some aspects of quality control/quality assurance tests for the maintenance tool.
As a result of the development of this LRS, Iowa DOT has seen several changes in business processes and functions. LRS has been advantageous to Iowa DOT in several ways, including the following examples:
- Verifying that all snow runs are covered and identifying missing snow runs.
- Determining snow route optimization.
- Facilitating a statewide effort for development of a sign inventory.
The Iowa Five Year Program, an effort sponsored by the DOT Office of Program Management, is using LRS to create project locations and provide shape and Google Earth files for public consumption.
Questions and Answer Session
Does the propagation manager cascade to events?
Business data is divorced from LRS. The only components that the LRS has in common with business data are those required by Location Referencing Methods (LRM). If Iowa DOT changes the LRS location that would affect the business systems with a LRS location, the business system can be notified. The system is interactive but this could change depending on the business needs of the organization. For example, if a sign location that is based upon a reference post changes because reference posts are moved or the route is changed, the LRS could automatically send a notification to the business unit maintaining the sign and change its location to represent current conditions. The datum reference location of the sign has not changed — only the reference post location associated with the sign has changed (it is still in the same geographic location).
Does the LRS automatically store data?
Not at this time. However, there would be a number of ways to do that if the business system required it.
What is TIG?
TIG is the AASHTO Technology Implementation Group (TIG). The AASHTO TIG looks for innovative technologies and applications to share with interested agencies nationwide. TIG identified the Iowa DOT as the lead agency to promote LRS.
How do you deal with network changes when you parsed the plow crew data?
Maintenance did not have to deal with dates in the system — they only wanted to validate the locations of plow crews and how many staff it required to ensure that they were neither understaffed nor overstaffed.
What were the total costs and amount of time it took to implement LRS?
Iowa DOT implemented a pilot project for LRS in 2001. It took 1.5 years to complete the pilot. Next, Iowa DOT digitized the road network, which took about 2 years. Besides the purchased components such as Oracle, many of the tools used to build the LRS were available from Iowa DOT at no cost. The total cost for the LRS was $5.5 million.
Has the TIG made any progress on integrating ESRI products into the upper tier of your LRS?
No, although Iowa DOT is looking for partners to invest in creating an ESRI top tier to work with the bottom and miple tiers. Iowa DOT is waiting for a state or states that may have a need for the ESRI top tier to step forward and take the lead in this development.
How do you locate point assets, particularly at intersections?>br />
We have built many things into the physical implementation of the model. The LRS aggregation feature can aggregate multiple features into a single feature with a unique identification. If you wanted to make a complex intersection, into a single feature because of business requirements, the Iowa LRS would support this requirement.
Can you clarify the traveled way LRS and roadway LRS?
On the traveled way LRS, everything is located in the direction of travel, whether the roadway is divided or not. LRS runs in both directions. The maintenance tool can create a route path that includes all the ramps and there is no abstraction. The route follows the true path and goes all the way to the tapers to apress maintenance needs. The tool also allows for the creation of a centerline abstraction of divided traveled ways called a roadway.
Is Iowa DOT aware of other states using Oracle for a LRS?
Wisconsin and California.
What is the benefit of using Oracle for the LRS?
Oracle can provide a way to do queries without using a GIS. Iowa DOT can pull data from an Integrated Database Management System (IDMS) database and use a native SQL to do the LRS transformation and then store the data with geometry in Oracle, without any front-end presentation tier software. This is all done by Information Technology support staff. The end user just wants to see the geometry.
Do you have any interest in having a MicroStation/Bentley Map presentation tier?
You can connect MicroStation to Oracle and view LRS data.
What is the average element length?
The longest anchor section is 5.1 miles, which is based on statistical analysis.
How do you handle dividing a linear element into subsections when roadway features change within the linear features?
We purposefully separate the LRS from business data so the LRS can remain as pure as possible. We let business data divide into segments based upon business data requirements. Iowa DOT supports dynamic segmentation and is also in the process of integrating the roadway inventory data into a new database that will use the LRS for its location component.
Have you looked at integrating more of the LRS process within an Oracle environment?
Iowa DOT has not looked into that. We have worked with a spatial application programming interface (API) but it may not be cost-effective to re-engineer what we already have.
Can you comment on your accuracy of anchor points? Early on, you put pipes in the field. How do you collect them and what is level of precision?
Iowa DOT has a number of data sets that are statewide and we have aerial imagery with 1-meter of resolution. The majority of data collected for rural areas is at that resolution. We wanted to use aerial images since we have a wealth of this information. We got in the ground floor when Oracle starting aping spatial functionality. Anchor points should be within several meters.
Are you using open-source GIS to publish key markup language (KML) data? How are you integrating with Google Earth?
Oracle doesn't have a KML exporter, so we wrote one to export to KML. You can use GeoMedia or ArcGIS to export out. Using the service layer, they will read Oracle directly and output KML on the fly. We are also using web mapping services (WMS) and KML.
Have you made a transition from the route reference post to a route coordinate? Did you have people around the organization with route miles?
Our recommendation is to use coordinate routes. Some signs we maintain are off our system. We want to minimize the things that can go wrong with data collection. The system also contains route and milepost data. The problem with route mileposts is that data becomes outdated more quickly. We have had issues with maintaining the accurate location of mileposts.
Do you have a dollar figure for the Bentley and Intergraph software required?
LDMX runs about $20,000 and GeoMedia Professional runs about $8,500 per concurrent license. You will also need GeoMedia Transaction Manager at $7,000 per seat. It would useful to get more specific quotes from Bentley and Intergraph directly due to the complexity of different pricing packages and various required business needs.
To conclude the webinar, Mr. Sarmiento presented some other information and resources related to applications of GIS in transportation:
- The American Association of State Highway Officials (AASHTO) sponsors an annual GIS for Transportation (GIS-T) symposium. The 2009 symposium will be held in Oklahoma City, Oklahoma, from April 5-8. The AASHTO GIS-T symposium website is available at http://www.gis-t.org/index.php
- FHWA has developed a new quarterly GIS in Transportation newsletter to share information about significant geospatial transportation news, events, and applications. Newsletters are available at http://www.gis.fhwa.dot.gov/newsletters.asp
- FHWA's GIS in Transportation website highlights innovative uses of GIS for transportation and offers related information, opportunities, and resources for sharing uses and applications of GIS. The website is available at https://www.gis.fhwa.dot.gov/
- The next webinar in the FHWA-sponsored GIS in Transportation webinar series will occur in approximately three months. Details for the future event and other upcoming webinars will be publicized on the GIS-T yahoo group distribution list, in emails to State DOT GIS managers, and on FHWA's GIS in Transportation website.
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