Automated LiDAR Data Quality Control

Engineering | Architecture | Design-Build | Surveying | GeoSpatial Solutions
Automated LiDAR Data
Quality Control
February 12, 2013

Copyright © 2010 Merrick & Company All rights reserved.
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Presenter
Matt Bethel, GISP
Director of Technology for Merrick & Company
Development Manager for Merrick’s Advanced
Remote Sensing (MARS) software

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Merrick & Company Office Locations
500 employees at 13 national
and 4 international offices

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Merrick’s International Project Experience

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Presentation Objective
This presentation will review an automated approach to
airborne LiDAR quality analysis and quality control (QA/QC)
that is based on the USGS’ National Geospatial Program
LiDAR Base Specification Version 1.0. It will showcase a fully
automated process for analyzing LiDAR data in its entirety to
verify and report compliance to a project’s acceptance criteria.

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 http://pubs.usgs.gov/tm/11b4/TM
11-B4.pdf
 Intended to create consistency
across all of USGS’ National
Geospatial Program (NGP)
funded LiDAR data collections, in
particular those undertaken in
support of the National Elevation
Dataset (NED)
 Unlike most other “LiDAR specs”,
which focus on the derived bare
earth digital elevation model
(DEM) product, this specification
places unprecedented emphasis
on the handling of the source
LiDAR point cloud data
USGS NGP Lidar Base Specification Version 1.0

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Who should have LiDAR QA/QC concerns?
 Data providers: to ensure that data meets project
specifications prior to delivery
 Client/End users (commercial entities, local/state/federal
organizations): to ensure that they are receiving the products
that they purchased and require for their specific needs
 Any purchaser of LiDAR data that requires a reliable process
to determine if final payment should be authorized

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The Problem – Client Side
 RFPs and project scope of works state accuracy
requirements but…
 rarely say anything about how they will test these requirements
 usually talk about absolute accuracy but not always relative
 sometimes contradict themselves (“+/-15cm RMSEz at the 95% C.I.”)
 are often copied from other documents and the client is left not really
knowing what they are asking for or understand what they are getting
 most everyone is asking for something slightly different
 USGS Lidar Base Specification Version 1.0
 “We want that”
 “We want pieces of that”
 “We want to refer to that but ask for this”

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The Problem – Vendor Side
When contracted to QA LiDAR projects, we have seen a rise in poor
quality data as a trade off to push the bidding price down
 Data providers vary the procedure, frequency, and extent of their LiDAR calibration
 Many vendors use automated boresight tools which could have potentially negative
outcomes:
 Lower skill level required
 Effective enough to be dangerous
 Most do not consider all aspects of an error budget
 Does not always find and flag flight planning or acquisition issues, sensor malfunctions, or
human mistakes
 Often times, little to no QA/QC procedures
 Some ‘cheat’ to get around proper calibration and other QC tasks
 Clipping off or reclassifying edge lap to avoid dealing with LiDAR boresight
 Shifting tiles to a custom geoid derived from the vertical error to ground control
 Some vendors can hide error through other creative techniques especially if they discover
problems after the plane has left the jobsite
 These practices can be caught and/or avoided

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The Problem – Quality
 QA/QC methodologies ranged from…
 None
 Checking a representative sample (what happens everywhere else?)
 Checking some things but not others (i.e. absolute accuracy but not
relative calibration)
 Throwing many people and a lot of time at projects to manually check
as much data as possible (or that budget will allow)
 Contract it out, typically it’s done right but at added costs and delays
 Clients rarely know how to properly review LiDAR data nor
do they have the tools to do so
 We needed more automated tools to get quality answers
quickly and accurately about our LiDAR data

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Our Goals
 To check all airborne LiDAR data in an automated fashion
 Make it work across sensor platforms
 Make it accurate
 Make it usable
 Make it customizable
 Make it fast
 Provide quantitative and qualitative results, whenever possible
 When this is impossible, create derivative products during the automated
process that will help the user QC the data as quickly and thoroughly as
possible
 Create tools that catch problems before they are too late
 Create links to supplemental data that can assist with the QC process
 Create reports that the end user can understand
 Deliver these reports to the client or empower them to perform automated
QA/QC analysis on their own data
 Provide this tool to end users that have these challenges

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MARS Tool Development
 We developed many stand alone tools in
MARS to analyze and report many
aspects of LiDAR QA/QC
 Control reporting tools (absolute accuracy)
 Flight line vertical separation rasters (relative
accuracy)
 Point density reporting
 Spatial distribution verification
 Hillshade to check LiDAR filter
 LAS statistics
 Intensity/range analysis
 Void detection
 Others
 These tools run on the entire dataset and
often produce a report or a single,
manageable, output raster, compressed to
a JPEG2000 format for fast display and
small file size
 Excluding control point reporting, the
products of these tools report on all of the
data, not a representative sample

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Modularization and Automation
 We built a module in MARS that
combines our stand alone tools
into an automated process that
test for the 29 USGS LiDAR
specification V1.0 items
 This creates two PDF reports
(detailed and summary) plus
subsequent derivative products
 It is batched and performance has
been optimized to run on large
data sets
 Multi-threaded
 Effective RAM utilization
 Temporary local disc caching for
slower network processing needs
 It is customizable so that some or
all of the tests can be processed,
depending on the need or
available input data
 Output report and derivative data
are both thematically rendered
and statistically reported

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Results
 A comprehensive and automated approach to checking the quality
of all LiDAR point file deliverables in their ENTIRETY – no
representative sample testing
 A tool that saves an enormous amount of manual QC labor hours
and dollars
 A workflow addition that eliminates costly rework and project
delays
 A process for data providers to deliver better products (first time
delivery acceptance) and invoice the customer sooner
 A tool for end users to understand what level of data quality they
are receiving and be able to provided proof of required rework.
This also educates the client about their data investment.
 A mechanism for clients to decrease the delivery acceptance
period and start using the data sooner

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Performance Benchmarks
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100 120
Runtime
(hours)
LiDAR Data Size (GB)
MARS QC Module Benchmark Results
 Run times depends on:
 Data
 LiDAR flightline distribution
 Flightline overlap
 Project boundary complexity
 Number of project boundaries
 Number of delivery tiles
 LiDAR density
 Land cover
 Processing computer hardware
 Number of CPUs
 Amount of available RAM
 Disc / network speed
 Settings
 All tests run versus selected tests
 Optional derivative data produced
 Very rough processing speed (data ratio to
processing time) is ~3 GB per hour on a high
end processing computer (8-16 CPUs and
12-48 GB of RAM)

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Report Demo

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Future Developments
 Workflow staged processing
 Coverage check
 Boresight
 Filter
 Delivery
 Distributed processing
 More user definable LiDAR QA/QC tests
 Additional LiDAR specifications
 Horizontal accuracy measurement and
reporting capabilities

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Thank you
Matt Bethel
Director of Technology
Merrick & Company - Booth #45
matt.bethel@merrick.com
303-353-3662
http://www.merrick.com/Geospatial
http://www.merrick.com/Geospatial/Services/MARS-Software

Automated LiDAR Data Quality Control

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