14.0 CONSIDERATIONS FOR COMMON MOBILE LIDAR APPLICATIONS
14.4.1 Construction automation, machine control, quality control (1A)
- See discussion for Engineering Surveys
- MLS can obtain data for use in design and machine control. However, during construction the MLS will still require a navigable path to acquire data.
- Change detection and deviation analysis software are emerging, which can input design models and highlight deviations from a MLS point cloud for construction quality control.
14.4.2 As-built/as-is/repair documentation (1A)
- See discussion for Engineering Surveys
- MLS can provide detailed documentation for as-builts or repairs compared to traditional “red lines” notated on paper plans. When the data are integrated into a centralized database that is continually updated, they can be very valuable in future planning and projects.
14.4.3 Quantities (1C)
- For earthwork quantities, tops and some sides of stock piles may not be obtained with MLS due to visibility constraints. Static scanning can often be used to supplement.
- MLS data can be used to determine lengths, areas, volumes, and number of features for other quantities such as painted length of striping or areas of pavement patching.
14.4.4 Pavement analysis (1A)
- Yen et al. (2011) found that typical MLS did not yet meet Caltrans standards for pavements.
- Local accuracy is critical; network accuracy is less stringent except for time-series comparisons. Particularly, local vertical accuracy is critical (sub-mm).
- Pavement smoothness evaluation requires high sampling intervals (1-4”) and accuracies (sub-mm vertical). Many generic MLS will not sufficiently meet these requirements, although data collected at higher resolutions (e.g., >1,000 points/m2) can be statistically filtered to improve vertical accuracies by removing some noise. However, there are some specialized systems that focus solely on capturing pavement for short sections that can meet these requirements for local accuracy.
- Current resolution capabilities may not enable full analysis of small cracks (mm-level widths). However, larger cracks and potholes can generally be observed clearly in the point cloud and imagery.
14.4.5 ADA compliance (1A)
- See the CAD\baseline models and Quality Control discussions.
14.5.1 Structural inspections (1A)
- See discussion for CAD\baseline models
- Bridge inspections will require a higher degree of accuracy and detail compared to other structures.
- While MLS can provide overall geometric information and a gross condition assessment, critical connections and details of bridges will likely not be captured with MLS due to visibility constraints. Hence, field inspections should not be replaced by MLS.
14.5.2 Drainage (1A)
- Slopes and elevations can be readily extracted from MLS data to support drainage analysis. However, MLS data enables analysis of localized depressions where water can pond.
- In areas where water ponding is a problem, MLS scanning should be done when it is dry to ensure adequate coverage of the road surface.
14.5.3 Vegetation management (2C), power line clearance (2B)
- See discussion on Virtual, 3D design regarding clash detection.
- See discussion on Clearances.
- Time series MLS data can be used to track growth rates as well as highlight areas of encroachment near the roadway or power lines.
14.6.1 Emergency response (3C)
- MLS data will generally be used to create baseline models to feed into a GIS or TIM for emergency response use.
- In a post-disaster situation, MLS can be used to acquire data rapidly along a damaged section (provided it is still navigable) with a small field crew. This can then be virtually navigated by response personnel to determine appropriate courses for action (e.g., when to open the road to traffic, what repairs are needed).
14.6.2 Clearances (1A)
- Requires high local accuracy, network accuracy is not as critical.
- The resolution of MLS enables clearance analysis to be performed across the entire section rather than at a few select locations, improving the likelihood of finding the minimum clearance.
- MLS provides a dataset that can be used for virtual clash detection of objects (of any shape) for clearance analysis.
- MLS can be developed into a Transportation Information Model (TIM) so that clearances can be quickly obtained along an entire route when permits need to be issued.
- Software packages are available to determine clearances automatically from point clouds. However, it is always important to verify results of automated algorithms.
14.6.3 Traffic congestion\ parking utilization (3C)
- These studies require the scanner to move faster than traffic. For example, if traffic is backed up in the northbound lanes, the scanner can be travelling in the southbound lanes and collect data for the northbound lanes, assuming the cars are visible.
- Multiple, repeat passes are needed throughout the day/week for the study.
14.6.4 Land use\zoning (3C)
- MLS can provide information to support land use and zoning studies. However, it should be combined with airborne LIDAR data since MLS can only obtain data available from the road.
14.6.5 BRIM\BIM (3C)
- Models extracted from point cloud data will generally be geometric primitives. For example, deviations such as curvature from planar surfaces will be lost in the BIM\BRIM models unless significant effort is put into using non-standard model shapes.
- BRIM\BIM modeling enables attributes/ intelligence to be assigned to the data. However, these are often assigned manually or semi-automatically and are not directly available in the native scan data.
- Techniques are in development to automatically verify, update, or correct BRIM/BIM models using static LIDAR data (Tang et al. (2012)). These will likely be expanded to MLS data.
14.7.1 Extraction of geometric properties and features for safety analyses (2B)
- MLS point clouds can be used to obtain common geometric information (grade, slope, width of road\lanes, location of signs, etc.) for visibility and other safety analyses (e.g., stopping sight distance).
- Safety investigations can be done virtually within the 3D point cloud.
14.7.2 Forensics\accident investigation (2A)
- For post-disaster surveys, crashed vehicles may block necessary views of the scene, so static scanning will generally be a better choice.
- However, routine MLS surveys can provide detailed information of road surface characteristics (grade, slope, width, etc.) to support forensic analysis.
- MLS data can also be used to support other forensics investigations such as retaining wall failures. Repeat surveys can be important to reconstruct failure mechanisms and establish timelines.
14.7.3 Driver assistance\ autonomous navigation (2B)
- MLS data can provide input models used by driver assistance and autonomous navigation systems.
- Many driver assistance systems also incorporate on-board LIDAR sensors.
14.8 Asset Management
14.8.1 Asset management\modeling & inspection\inventory mapping\GIS (3B)
- See discussion for CAD\Baseline models.
- Attributes will need to be applied through manual or semi-automatic processes using data from other sources.
14.8.2 Sign (2B) \ billboard (3C) inventory
- Semi-automatic and automatic processes exist for extracting signs.
- Appropriate point cloud density may be difficult to achieve on a sign, however, imagery provides more detail.
- The reflective nature of many types of signs may lead to problems with saturation and blooming effects.
- Depending on the orientation of the scanner, some configurations will not actually capture both the front and backs of the signs.
- Intensity measurements provide an indication of a sign reflectivity, but are not standardized measures. They are generally only comparable within a dataset or datasets collected with the same system.
- Simultaneous image capture is a necessary requirement for sign inventory projects.
14.9.1 Virtual tourism (3B)
- Many transportation agencies provide highway maps for tourists. Potentially MLS data could be used to create online virtual maps of the state highways so that drivers can see virtually visit sections of the route, similar to online street view mapping programs.
- Drivers could also virtually “drive” difficult interchanges when planning their routes.
14.9.2 Historical preservation (1B)
- MLS can be useful for acquiring virtual models of historic districts. However, static scanning will be preferred for individual structures of interest.
14.10.1 Unstable slopes (1B) \ landslide assessment (1B) \ coastal change (2B)
- Many times MLS data will need to be supplemented by static or airborne scan data for these studies. For example, when the road is on a slope, the MLS system will be able to acquire data on the uphill portion of the slope visible from the road (although coverage may be sparse near the top, depending on the slope and road geometry), but will not be able to acquire data on steep, downhill slopes that cannot be seen from the roadway.
- MLS can be used for small landslides and slopes, particularly when these slopes are steep. However, large landslides will require airborne LIDAR.
- In addition to geometry, intensity values from MLS data can often be helpful to distinguish between sediment types in outcrops.
- The accuracy and resolution required will depend on the speed at which the landslide is moving. In addition to spatial resolution, temporal resolution (i.e., how often repeat scans are conducted) should also be considered.
- Control points and objects near landslides can move and may not be reliable.
Next Section >> Chapter 15: Information Management