Understanding LIDAR Understanding LIDAR Technology Technology

Brian Mayfield, CP, GISP, GLS

Timothy A. Blak, GS, PLS, CFM

Brief IntroductionsBrief Introductions Brian Mayfield, CP, GISP, GLS

Dewberry Program Manager to VGIN

Tim Blak, GS, PLS, CFMAppendix 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)

Our Role in the IndustryOur Role in the Industry Trusted Advisor

North CarolinaMaryland

Mapping Solutions ProviderUSGS GPSCNOAA CSCFEMA Regional IDIQ Study Contractor

Not a Mapping FirmNo Acquisition Resources (not tied to any specific

technologies or brands) Industry Leading QA/QC Services

NOAAStatewides

What is LIDARWhat 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

What LIDAR is NOTWhat LIDAR is NOT All-weather

Target must be visible within the selected EM spectrum

No rain or fogMust be below clouds

Able to “penetrate vegetation”LIDAR can penetrate openings in the vegetation

cover but cannot see through closed canopies

AnimationAnimation

LIDAR ComponentsLIDAR Components Three major

components of a LIDAR system

1. GPS

2. Inertial Measurement Unit

3. Laser Range Finder

Laser ReturnsLaser Returns First

Ideal for surface models

LastIdeal for generating bare-earth terrain models

IntermediateIdeal for determining vegetation structure

Laser ReturnsLaser Returns

Return Pulses

Incoming Pulse0

20

Time(nanosec)

0

40

60

80

100

120

140

20

Return#1

Return#2

Return#3

Return#4

Return Pulses

Incoming Pulse

Return Pulses

Incoming Pulse0

20

Time(nanosec)

0

40

60

80

100

120

140

20

Return#1

Return#2

Return#3

Return#4

0

40

60

80

100

120

140

20

Return#1

Return#2

Return#3

Return#4

Courtesy of EarthData Technologies

LIDAR data points - X, Y, ZLIDAR data points - X, Y, Z

Top View

Side View Courtesy of Terrapoint

Intensity ImagesIntensity 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)

Intensity ImageryIntensity Imagery

Full Point Cloud Surface ModelFull Point Cloud Surface Model

Surface ModelSurface Model

Cityscape Surface ModelCityscape Surface Model

Cityscape Ground ModelCityscape Ground Model

Full Point Cloud Surface ModelFull Point Cloud Surface Model

LIDAR UsesLIDAR Uses

Courtesy of Terrapoint

LIDAR UsesLIDAR Uses

Accuracy StandardsAccuracy Standards FEMA – Guidelines and Specification for

Flood Hazard Mapping Partners Appendix A: Guidance for Aerial Mapping and Surveying

NDEP Guidelines For Digital Elevation Data

FEMA’s Criteria for Topographic FEMA’s Criteria for Topographic DataData

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)

Accuracy EquivalenciesAccuracy Equivalencies

NMASContourInterval

NMAS90%Conf

NSSDA95%Conf

NSSDARMSEz

2’ 1’ 1.2’ 0.6’18.5 cm

4’ 2’ 2.4’ 1.2’37.0 cm

Quantitative Verification Quantitative Verification NDEP Standards as of Jan. 2003NDEP 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.

ContoursContours 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”

ContoursContours

Two Types of Contours1. Engineering

2. Topographic

LIDAR ContoursLIDAR Contours

BreaklinesBreaklines 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

PricingPricingApproximate Costs Per Square Miles Sq Miles - Tw o Foot Equivalency

0

200

400

600

800

1000

1200

20 50 100 200 500 1000

Sq Miles

Questions?Questions?