Understanding LIDAR Technology

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Understanding LIDAR Technology

• Brian Mayfield, CP, GISP, GLS
• Timothy A. Blak, GS, PLS, CFM

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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_Ver
  1_10May2004.pdf)

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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

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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

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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

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Animation
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LIDAR Components

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

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Laser Returns

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

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Laser Returns
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LIDAR data points - X, Y, Z
Courtesy of Terrapoint
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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)

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Intensity Imagery
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Full Point Cloud Surface Model
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Surface Model
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Cityscape Surface Model
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Cityscape Ground Model
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Full Point Cloud Surface Model
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LIDAR Uses
Courtesy of Terrapoint
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LIDAR Uses
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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

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FEMAs 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)

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Accuracy Equivalencies
NMAS Contour Interval NMAS 90 Conf NSSDA 95 Conf NSSDA RMSEz
2 1 1.2 0.6 18.5 cm
4 2 2.4 1.2 37.0 cm
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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.

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Contours

• Once the elevation model is created - contours
  are just a click awayor 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

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Contours

• Two Types of Contours
• Engineering
• Topographic

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LIDAR Contours
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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

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Pricing
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Questions?