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Understanding LIDAR Technology

Understanding LIDAR Technology . Brian Mayfield, CP, GISP, GLS Timothy A. Blak, GS, PLS, CFM . Brief Introductions. Brian Mayfield, CP, GISP, GLS Dewberry Program Manager to VGIN Tim Blak, GS, PLS, CFM

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Understanding LIDAR Technology

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  1. Understanding LIDAR Technology Brian Mayfield, CP, GISP, GLS Timothy A. Blak, GS, PLS, CFM

  2. Brief Introductions • Brian Mayfield, CP, GISP, GLS • Dewberry Program Manager to VGIN • Tim Blak, GS, PLS, CFM • Appendix A of the Map Modernization Guidelines (http://www.fema.gov/pdf/fhm/frm_gsaa.pdf) • NDEP (National Digital Elevation Program) Guidelines for Digital Elevations Data (http://www.ndep.gov/NDEP_Elevation_Guidelines_Ver1_10May2004.pdf)

  3. Our Role in the Industry • Trusted Advisor • North Carolina • Maryland • Mapping Solutions Provider • USGS GPSC • NOAA CSC • FEMA Regional IDIQ Study Contractor • Not a Mapping Firm • No Acquisition Resources (not tied to any specific technologies or brands) • Industry Leading QA/QC Services • NOAA • Statewides

  4. What is LIDAR • LIght Detection And Ranging • Active Sensing System • Uses its own energy source • Measures range distances • Based on time between emission, reflection and receive time • Direct terrain measurements, unlike photogrammetry which is inferred • Day or night operation except when coupled with digital camera • LiDAR provides a point cloud with X.Y,Z positions

  5. What LIDAR is NOT • All-weather • Target must be visible within the selected EM spectrum • No rain or fog • Must be below clouds • Able to “penetrate vegetation” • LIDAR can penetrate openings in the vegetation cover but cannot see through closed canopies

  6. Animation

  7. LIDAR Components • Three major components of a LIDAR system • GPS • Inertial Measurement Unit • Laser Range Finder

  8. Laser Returns • First • Ideal for surface models • Last • Ideal for generating bare-earth terrain models • Intermediate • Ideal for determining vegetation structure

  9. Courtesy of EarthData Technologies Laser Returns

  10. Top View Side View LIDAR data points - X, Y, Z Courtesy of Terrapoint

  11. Intensity Images • Measures the amount of light returning to the sensor • Developing technology – infancy stage • Can now be used for stereo-compilation to generate 3D breaklines (“LIDARgrammetry)

  12. Intensity Imagery

  13. Full Point Cloud Surface Model

  14. Surface Model

  15. Cityscape Surface Model

  16. Cityscape Ground Model

  17. Full Point Cloud Surface Model

  18. LIDAR Uses Courtesy of Terrapoint

  19. LIDAR Uses

  20. Accuracy Standards • FEMA – Guidelines and Specification for Flood Hazard Mapping Partners Appendix A: Guidance for Aerial Mapping and Surveying • NDEP Guidelines For Digital Elevation Data

  21. FEMA’s Criteria for Topographic Data For either photogrammetry or LIDAR: • Accuracy equivalent to 2’ contours or better for flat terrain (Accuracyz = 1.2’ at 95% confidence level) • Vertical accuracy at 95% confidence level = Accuracyz = 1.9600 x RMSEz • Accuracy equivalent to 4’ contours or better for rolling to hilly terrain (Accuracyz = 2.4’ at 95% conf level)

  22. Accuracy Equivalencies

  23. Quantitative Verification NDEP Standards as of Jan. 2003 Fundamental Vertical Accuracy. For open terrain only, compute RMSEz. Report Accuracyz as: “Tested __ (meters, feet) Fundamental Vertical Accuracy at 95% confidence level in open terrain based on RMSEz x 1.9600.” Supplemental Vertical Accuracy. For all other land cover categories, determine 95th percentile error(s). Report Accuracyz as: “Tested __ (meters, feet) Supplemental Vertical Accuracy at 95th percentile in weeds, crops, scrub, forests, urban areas, etc.” and document outliers. AND/OR Consolidated Vertical Accuracy. Report Accuracyz as: “Tested __ (meters, feet) Consolidated Vertical Accuracy at 95th percentile in open terrain, weeds, crops, scrub, forests, urban areas, etc.” and document outliers.

  24. Contours • Once the elevation model is created - contours are just a click away…or are they? • The key to creating good contours is to control their behavior • Controlling their behavior can be expensive using traditional methods • New methodologies are being developed for LIDAR such as hydro-enforced contours or by “LIDARgrammetry”

  25. Contours Two Types of Contours • Engineering • Topographic

  26. LIDAR Contours

  27. Breaklines • Linear features that control surface behavior • Can be 2D or 3D • Traditionally derived from stereo photogrammetry or from surveys • Can use LIDAR and Intensity to create breaklines or can use Hydro-enforced method

  28. Pricing

  29. Questions?

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