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Appropriate planning for mobile lidar
projects can have a great impact on
success. This white paper offers engineers
numerous pragmatic best practices for the
successful execution of mobile lidar
projects.
Best
Practices for
Planning a
Mobile Lidar
Project 2013
Copyright © 2013 Continental Mapping Consultants, Inc. All Rights Reserved
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Top 10 Tips for Planning a Mobile Lidar Project
© Continental Mapping Consultants, Inc. - 2013 3
No portion of this report may be reproduced or distributed in any form or by any means without the prior written permission of the authors.
Lidar is rapidly becoming the tool of choice for state departments of transportation to develop high accuracy terrain models for engineering design. Mobile and terrestrial lidar platforms, as opposed to airborne platforms (fixed wing or helicopter), are quickly becoming the preferred tool for data collections. While the jury is still out on exactly which platform provides the best return on investment, vehicle mounted systems will continue to surge in popularity because of their relative ease of deployment.
Mobile lidar acquisition, like all laser scanning, is still a “line of sight” tool, and project designs need to compensate for this. For a typical transportation design project, somewhere between 5-25% of the area within the project limits will require some sort of infill technique regardless of the tools or techniques used. Surveyors are restricted by private property access and physical obstructions, aerial photogrammetry and lidar can’t see through trees, and terrestrial and mobile platforms can’t see behind buildings and have angle of incidence and distance limitations. For a number of reasons, it is wise to take a technology and platform agnostic viewpoint when designing a data collection project. The first priority is to clearly understand the business and engineering needs, and then decide on how you will approach data collection.
Sample mobile lidar collect of an urban corridor
Top 10 Tips for Planning a Mobile Lidar Project
© Continental Mapping Consultants, Inc. - 2013 4
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With that in mind, the following list offers tips on how to properly design and constrain a mobile lidar project so that it meets typical engineering design needs.
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 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
Continental Mapping’s Riegl VMX-250 mobile lidar
sensor
Top 10 Tips for Planning a Mobile Lidar Project
© Continental Mapping Consultants, Inc. - 2013 5
No portion of this report may be reproduced or distributed in any form or by any means without the prior written permission of the authors.
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 control targets and referencing this control to the appropriate reference network. Sound survey technique, proper documentation, and metadata 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, as of February 2013, none of these are fully adopted and accepted for transportation engineering design at the state DOT level. Therefore, you are on your own to some extent 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. To understand this further, see our Transportation Information Modeling best practices video on our YouTube channel here.
Top 10 Tips for Planning a Mobile Lidar Project
© Continental Mapping Consultants, Inc. - 2013 6
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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.
Options for transportation information modeling
Top 10 Tips for Planning a Mobile Lidar Project
© Continental Mapping Consultants, Inc. - 2013 7
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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.
Extracted 3D features shown over imagery collected by the lidar sensor
Top 10 Tips for Planning a Mobile Lidar Project
© Continental Mapping Consultants, Inc. - 2013 8
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Use These Links for More Information on Continental Mapping
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Call Continental Mapping as you consider lidar technology for your engineering projects. We hold two master services contracts for photogrammetry, lidar, and related services with the Wisconsin DOT, and we understand where they are headed with the new MAP-21 requirements and MAPSS evaluation criteria. We also understand the complexities of adopting new technologies and techniques in design workflows and our experienced in guiding newcomers through the process—we have even helped WisDOT with this! Hopefully, the best practices presented in this paper have provided you a foundation to build upon. We welcome your comments and questions on this paper. Don’t hesitate to contact us!
www.continentalmapping.com 888.815.3327
