Mobile lidar scanning offers a flexible survey-grade data collection method that requires less survey crew time on the road (in harms way), fewer site visits, and cheaper mobilization costs, while providing a safe alternative to traditional surveying and aerial collection. Mobile scanning is ideal for long transportation or utility corridors, capable of collecting very high accuracy data and video at posted highway speeds.
These are the tips we provide clients looking to plan a mobile scanning project.
Tip 1 — Evaluate the Three Cs: Currency, Clarity and Content
When planning a project, it is critical to evaluate existing data and requirements from the perspective of currency, clarity, and content. How current is the existing information and what is the requirement? What imagery resolution and/or DTM accuracy is needed? What items are critical to my design and how do I need them represented? Be realistic on those items that drive cost — just because it would be nice to have 0.05-foot accuracy does not mean it is necessary for your design.
Tip 2 — Know Your (Project) Limits
Often, project limits are defined and mapping data specifications are referenced to that project limit. Often, however, the critical area within that limit is far smaller. Those that take care in evaluating their project limits, and then pre-define critical, non-critical, and referential areas within that limit can realize significant savings on unnecessary data collection and processing. This step is typically as simple as using Google Earth or and Bing Maps or doing proper field reconnaissance.
Tip 3 — Critical or Referential?
Differentiate between critical data and referential data. That is, know the difference between what you need mapped, measured, and modeled. These early assumptions have a ripple effect of downstream consequences. When done poorly, multiple field revisits, delayed schedules, and poor design decisions occur. Just as importantly, over-engineering the data collection requirement can make competitive job pricing difficult. Rather, choose the right tools and techniques, design a coordinated deployment with the goal of only one field visit, and validate the accuracy and completeness of the data collected prior to using it for derivative product development (DTM/PLAN/3D model elements).
Tip 4 — Research Your Client’s Requirements
All large government entities have ready access to their facilities development manual (FDM) or similar set of specifications. These documents are more fluid than many believe, especially as they relate to emerging technologies like mobile lidar. These requirements also have specific survey and mapping sections that many engineers and designers don’t pay much attention to. Designate a lead to read and understand these requirements. Knowledge of applicable specifications will help guide and properly constrain your design.
Tip 5 — Tie It Down/Write It Down
Good project design for any survey requires proper georeferencing. Mobile lidar, even though supplemented with GPS and inertial measurement unit (IMU) systems, still needs to be checked against higher accuracy reference points. This means establishing visible registration points and referencing this primary control to the appropriate reference network. Sound survey technique, proper documentation, and meta-data are critical.
Tip 6 — Evaluate Your Infill Requirements
Nearly every transportation design survey and mapping project requires 15% (+/-10%) infill. There are accepted and reasonable methods for inferential approaches for infill that do not require redeployment to the field. If the critical and referential elements are understood up front, these elements can be dealt with in the field and all that will be left are the referential infill needs that can use inferential techniques. This saves time and money, but requires extra rigor in design and different field flagging, marking, and collection techniques.
Tip 7 — Take the Time to Understand CIM/BIM/TIM
A multitude of draft mobile requirements are currently available. Civil, building, and transportation information modeling (CIM/BIM/TIM) specifications are available from organizations such as the Transportation Research Board (TRB), US Army Corps of Engineers (USACE) and several DOTs. However, these standards are in a fluid state of full adoption into transportation engineering design at the state DOT level. Therefore, there is some ambiguity in defining derivative mapping products extracted from a mobile lidar point cloud. Understanding level-of-detail (LOD) concepts on what and how to model from a point cloud to meet design requirements is critical.
Tip 8 — Properly Train Your CADD Staff
The software to manage and manipulate lidar point clouds is evolving quickly but our ability to acquire lidar data still exceeds the software industry’s ability to fully utilize it. However, proper training of your CADD staff can help. More than just software, consider training your CADD staff on the whole picture including: CIM/BIM/TIM requirements and best practices, client specifications, existing specifications and practical applications of 3D design concepts. It’s easy to get lost in the details when deriving mapping products from terabytes of lidar data. Continental Mapping has seen firsthand how inexperienced CADD techs can spend many hours modeling a single feature.
Tip 9 — Give Your Surveyors More Tools
Many engineering firms have land survey capabilities or utilize land survey to collect the data they need. In today’s market where clients want more value, traditional land survey alone can sometimes fall short. Mobile lidar supplements and supports your survey line of business. Proper control is still needed to obtain very high accuracies and blind spots must still be captured by field survey crews. Combined, however, mobile lidar and land survey offer an entirely new level of richness that supports the design process and provides a much richer dataset.
Tip 10 — Get the Supporting Imagery
Collecting supplemental imagery as part of the mobile lidar acquisition can prove very beneficial both in the feature extraction process and later when questions arise with your design team. The imagery offers rich contextual information as well as the ability to return to a location to identify details in the point cloud or understand other site details.