In many cases, the Mobile LiDAR collections that Baker performs do not produce a new product or service. Rather, it is a new method for achieving something that the client has come to expect from a traditional survey. In these cases it is appropriate, and necessary, to follow existing standards and specifications to develop the product they are familiar with we are not reinventing the wheel when we deliver a design file or CAD drawing. However, projects that do present a new problem to solve, or development of a new deliverable, are the most interesting to tackle.
With that in mind, the following examples present a cross-section of varying projects completed to-date. In future posts, Ill delve into more complex assignments that required innovative solutions.
Perhaps the most common collections are for roadway projects, but depending on the application (planning or design) the project requirements can be significantly different. However, the comprehensive data captured during the field effort easily lends itself to be exploited numerous times over the life of a project, or continually leveraged for numerous projects.
We have completed a number of roadway design survey projects from Interstates, US highways, rural and urban streets to roads (or lack thereof) in the middle of no-where (80 miles to the nearest hotel). The process for collection is fundamentally the same for each type of roadway. The significant difference is with the client. Unless specifically requested, we do not simply turn over the hundreds of millions of points we collect on a given project most organizations are not yet equipped with the hardware and software to host, manage and utilize the massive Mobile LiDAR point clouds developed. Rather, we utilize those points to develop a product that our client is accustomed to receiving based upon their given standards and specifications. Each state transportation department (or individual districts) has guidelines for deliverables which may be MicroStation or AutoCAD; and could include additional formatting for CaiCe, GeoPak, In-Roads or other requirements.
Asset Inventory: Utility Mapping
The inherent nature of a Mobile LiDAR collection lends itself well to corridors. Whether transmission corridors or urban roadways, the high level of detail collected goes beyond single purpose applications. Recently, we surveyed a 108 mile corridor for the installation of fiber optic cable. Due to the right of way width and divided roadway configuration, both directions of travel were captured in a mere two short days. Over the ensuing two week period, a team of LiDAR processors extracted road details, utilities, buildings and a slew of other features. Our client was faced with an accelerated schedule for completion due to funding requirements. Since the subsequent engineering design for the corridor could not begin until the mapping was completed, it was vital that the mapping be completed quickly. Another highly attractive reason for using Mobile LiDAR was due to uncertainties in the final alignment. Since we captured both sides of the Right of Way, minor changes to the route alignment would require harvesting the mapping information from the point cloud rather than sending staff into the field.
In addition to the LiDAR data, ground-based photography was simultaneously captured from the vehicle. The imagery was a vital component for overall scene comprehension to our processing team, but played a larger role for the ensuing environmental assessment. Using the latitude and longitude of the image exposures, shapefiles and Google Earth KMZ files were developed to facilitate viewing of pertinent photographs from multiple platforms. By providing the street level photography of the entire corridor much of which had been newly reconfigured the environmental scientists could perform preliminary site assessments from their desktop to minimize or eliminate site visits.
Digital Elevation Modeling
As with aerial LiDAR datasets, Mobile LiDAR information is used in the development of Digital Elevation Models however at higher densities. We have performed several collections in support of flood modeling and storm water modeling. The challenge with Mobile LIDAR is the completeness of the data sets when addressing obscured areas how to capture data behind houses and other permanent structures that are inaccessible from the ground. The integration of aerial LiDAR, IFSAR and other remotely sensed datasets can help provide the complete picture.
When looking at localized flood or storm water modeling, the question that is always posed is why not just use aerial LiDAR since Mobile LIDAR data may contain laser-shadowing or data gaps? Often in older subdivisions (usually those that have higher occurrences of flooding), the storm water infrastructure is not in place catch basins, retention ponds, etc, and are typically closed drainage systems with culverts that are traditionally isolated to the front yard. Therefore, the high point density and vertical accuracy of Mobile LiDAR data will provide a more detailed approach to a localized issue, where its needed. Inches matter.
Much More to Come
Each of the project types described above barely scratch the surface of Mobile LiDAR applications. As time progresses, the content added to the forum will become more detailed. Please feel free to provide feedback and recommendations for future postings.