14.0 CONSIDERATIONS FOR COMMON MOBILE LIDAR APPLICATIONS
14.2 Project planning
14.2.1 General planning (3C)
- MLS data provides critical geometric information and spatial relationships to aid in planning decisions.
- MLS data can be virtually explored by planners to reduce the need for site visits.
14.2.2 Roadway analysis (3A)
- MLS data enables both qualitative and quantitative analyses of roadway quality, particularly when combined with imagery.
- Intensity measurements are very helpful in distinguishing between damaged (e.g., cracks, spalling, staining) and undamaged sections of concrete.
14.2.3 Digital terrain modeling (1A)
- See discussion of General Mapping/General Measurements and Modeling
- MLS is one of the fastest techniques to acquire data for a DTM of a road and surrounding area.
- Point cloud data is often subsampled or statistically filtered to create a DTM that will perform well in CAD or other engineering packages, which may not be designed for large datasets (e.g., file size, number of vertices).
- Breaklines will need to be extracted semi-automatically or manually, if desired.
- In many cases, TINS will actually be 2.5D datasets, not 3D. Hence, they will not model details on vertical surfaces (e.g., building, steep slope face) in the point cloud.
- While CAD and GIS software offers support for point clouds and high resolution TIN models, many engineering analysis and design packages may not support the high density TINs created by LIDAR. A few potential solutions are:
TINs with frequent, planar surfaces can often be significantly optimized to reduce the triangle count with minimal effects on the model accuracy using readily available software.
Rather than use the point cloud to create the TINs, one can use extracted breaklines from the full point cloud and then use the breaklines with a subsampled version of point cloud (similar to a photogrammetric process).
Dividing the overall dataset into individual tiles prior to creating the TIN may also help. However, some software may not be able to work with multiple tiles
- Higher densities will be needed to obtain ground points in areas of high vegetation. In some cases, the MLS system may not actually see the ground due to its oblique look angle.
- Natural terrain mapping (1C) will not require as high of resolution as pavement surfaces, particularly since sediment will erode or be deposited across natural terrain surfaces.
14.3 Project development
14.3.1 CAD models\baseline data (1B)
- See discussion on Modeling.
14.3.2 Virtual, 3D design (1A)
- See discussion for Engineering Surveys
- MLS data can be used for clash detection (checking for intersections of proposed objects with existing objects modeled in the point cloud).
- MLS data can also provide detailed baseline information for comparison of alternatives.
- For intersection upgrades, the driven MLS path should include all intersecting streets and directions and not just rely on a single pass on one road in one direction.