GIS/GPS/CAD
Asset Maintenance Management
GPS combines with LiDAR sensors to provide a cost-effective solution
By Dean Pottle, PLS

Increased use by travelers and commerce is putting tremendous pressure on existing roads, highways, and railways. Traffic congestion not only affects a timely arrival to our destination but it also affects our safety and the condition of this country's infrastructure. Because of our increased use, it becomes more difficult and costlier to perform regular maintenance of these systems though maintenance has become most critical. Recent train derailments, freight congestion on rail systems, and the conditions of our roads are some obvious examples of the consequences of this.
    To promote transport of people and goods, planners and engineers are looking for ways to increase the capacity of the existing transportation systems as an alternative to incurring the prohibitive costs of building new roads and tracks. For example, with the goal of increasing the capacity of the railways to shoulder more of the burden of moving freight and people around the country, the U.S. Department of Transportation (USDOT) is working with the rail industry to investigate ways of increasing the speed and capacity of freight and passenger trains.
    For vehicles and trains to run faster, the road and track conditions must be monitored and followed up with frequent maintenance. Broken pavement or bumps in the road encourage motorists to slow down because of the rough ride. These conditions also effect driving safety at higher speeds. Similarly, trains moving at higher speeds are affected by poor track conditions which impact their conditions more severely. It follows that roadways or railways that are used for high-speed travel must be in better condition.
    To efficiently maintain these corridors, engineers are beginning to use new tools to inventory and manage assets and facilities as well as conditions. Technologies have been developed that allow technicians to record pavement and track conditions while traveling along the road or tracks at normal speeds. The advantages of this mode of collection include cost savings, continued traffic flow and safety. The captured data allows engineers and maintenance people to not only locate existing problem areas, but also potential problems which require detailed inspection and preventive maintenance.
    For efficient use of this data, current condition information is compared to previous data sets to check for deteriorating conditions. It is also matched to existing features along the routes such as other road and rail crossings, bridges, and culverts. With all this related information, engineers are better able to assess the reasons for the conditions and more efficiently define a solution to remove the condition or minimize its effects.
    Along with increased computer power and software, GPS is playing a significant role in making asset maintenance management (AMM) possible. To precisely compare the various data sets to each other, accurate spatial references to the data sets must be made. This allows the subsequent aberrations in the condition or "smoothness" to be properly matched to one another and then positioned relative to other features such as drainage culverts that may impact that condition. Without accurate positioning, proper assessment of the data would be very difficult.
    GPS, under proper conditions, is ideally suited for asset inventory along road and rail corridors. If there are few obstructions to block or interfere with the L-Band radio signals from the GPS satellites, a survey quality GPS receiver is capable of collecting horizontal sub-meter quality locations of selected features when the satellite measurements are corrected in "real-time" or through post processing. Electronic data collectors that can be interfaced with the GPS receivers can also be configured to accept pre-defined attribute information during data collection and format an entire data set for an object for efficient input to an asset database. If kinematic GPS techniques are used, centimeter level horizontal and vertical accuracy for positioning is possible. This allows an operator to collect discrete data points to assist in drainage and grade analysis of the roads and tracks. While GPS data collection is efficient compared to conventional methods of data collection, it can prove time-consuming as it exposes the operator to safety concerns with traffic.
    GPS can also be interfaced with various other tools such as video, gyros, ultra-sonic devices, and reflectorless lasers to reference the condition and feature measurements used by transportation engineers in a more continuous mode of data collection. This type of data collection enables engineers to obtain important information very quickly and is less disruptive to traffic along a project corridor. In the continuous data collection process, the position information has to be precisely referenced to the condition data being collected. Disadvantages include interruptions to GPS positioning due to obstructions and the inability to assign attribute information to important features.
    John E. Chance and Associates (CHANCE) of Lafayette, Louisiana, has recently been involved in several engineering projects with the USDOT, Amtrak, and other public and private transportation agencies that required efficient capture of terrain and asset position information along busy rail corridors. The collected survey data was used to locate important features such as mileposts, track centerlines, road crossings, switches, bridges, electrification, and culverts for mapping purposes and development of Digital Terrain Models (DTMs) for engineering analysis.
    To complete the projects, CHANCE utilized its FLI-MAPª system. FLI-MAP is a helicopter-based survey tool incorporating precise positioning, platform attitude, optical imaging and scanning LiDAR sensors. LiDAR is an acronym that stands for Light Detection And Ranging. LiDAR is similar to RADAR, only using light to measure distances. The basic concept of the FLI-MAP system is that the helicopter flies over the corridor that is to be surveyed. The LiDAR sensor scans the terrain and objects directly below the helicopter at a rate of 8000 points a second with a scan width equal to the helicopter height above the ground. The terrain directly below and forward of the aircraft is imaged with high-resolution video cameras, and recorded with a digital time stamp. The output, including the video from the FLI-MAP system includes XYZ positions of the laser returns.
    In order to process and extract information from the FLI-MAP data, CHANCE has developed a software package called FLIP7. This is a Microsoft Windows 95 or NT 4.0 true 32 bit Windows application that merges the helicopter position and attitude information with the LiDAR sensor data and video imagery. The package provides full CAD (Computer Aided Drafting) capabilities "on top of" the LiDAR data, providing additional intelligence to the CAD drawing. FLIP7 in conjunction with the Windows' application, VcrController, controls special time code capable VCRs allowing the user to coordinate the video images with the processed LiDAR data to get a full multi-media presentation of the surveyed area. FLIP7 also provides a means to view and ortho-rectify the video images in an interactive mode to gain additional information from the high-resolution images.
    Through interaction with its clients CHANCE incorporated a sophisticated data-attributing scheme in FLIP7. Each layer contains drawing objects, which include points, polylines, and "groups" or collections of points and polylines. Each class of object can have its own user-defined set of unlimited attributes. Each attribute defined can have an unlimited number of pre-defined values. When the user extracts a point on a given layer, and has a user defined flag set, a dialog box appears with a data base entry table to be filled out. The fields have the predefined values available to be selected. A default value for each attribute can also be defined as well as simply editing the field with a new value. An example of this data entry scheme would be when a transmission structure is captured or extracted on layer "bridge," a data base entry table including attributes like, "# of tracks," "Design Type," "Bulkhead Type," or "Support Configuration". Predefined values for "material" like "steel," "concrete," or "Other" could be selected from a select list. This data base entry scheme greatly increases the reliability of the data captured by reducing simple mistakes like spelling and calling things by different names.
    The FLI-MAP data with the FLIP7 processing has allowed CHANCE's clients to extract important information without sending a survey crew into the field. In every case additional information has been extracted from the data set than was required in the original project specifications. The qualitative and quantitative nature of the FLI-MAP data has allowed engineers to analyze drainage conditions, measure distances between rails, measure clearances between overhead power lines or model any area along the survey corridor. With this capability, planners and engineers are able to more efficiently acquire important data that will impact the engineering and design process of increasing highway and railway capacity.

About the Author:
Dean Pottle, PLS, is operations manager of the Corridor Mapping Department at John E. Chance & Associates, Inc., headquartered in Lafayette, Louisiana. He may be reached at 318-237-1300.

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