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04/10/2023 MN GIS/LIS Spring Workshop Series
LiDAR Quality Control
Validating LiDAR Data
Tim Loesch
Minnesota Department of Natural ResourcesGIS Section
04/10/2023 MN GIS/LIS Fall Workshops
LiDAR QA/QC – Did I get what I paid for?
LiDAR = Massive quantities of dataLiDAR = Expensive acquisition costsLiDAR = File upon file upon file…LiDAR = Very accurate informationLiDAR = Lots of room for error
Client QA/QC is an critical part of the process
04/10/2023 MN GIS/LIS Fall Workshops
LiDAR QA/QC – Did I get what I paid for?
QA/QC ElementsValidating file(s) existence
LiDAR is delivered in tiles
Validation of data Schema Valid elevation values Visual exam for data defects Vertical accuracy verification
Based on Contractual Obligations
04/10/2023 MN GIS/LIS Fall Workshops
LiDAR QA/QC – Did I get what I paid for?
Tightly defined data delivery structureProvides a basis for comparisonDevelopment of automated validation routines
04/10/2023 MN GIS/LIS Fall Workshops
LiDAR QA/QC – Did I get what I paid for?
Step by Step ChecklistHelps with consistencyAllows for distribution of effortEnsures consistency of validationProvides record of work
04/10/2023 MN GIS/LIS Fall Workshops
LiDAR QA/QC – Did I get what I paid for?
Initial File Check-inAutomated routine checks for:
File existence (GDB, LAS, DEM, etc) Valid values Field validation
Produces table of results
04/10/2023 MN GIS/LIS Fall Workshops
LiDAR QA/QC – Did I get what I paid for?
DEM MosaicMosaic all DEMs to single rasterGenerate shaded relief
Provides excellent product for visual examinationDisplay techniques can reveal small irregularitiesWe visually inspect every tile!
04/10/2023 MN GIS/LIS Fall Workshops
LiDAR QA/QC – Did I get what I paid for?
Generate derived products2’ ContoursBuilding Polygons
Can highlight problems that you cannot see
Classification errorsOverlap errors
04/10/2023 Minnesota Department of Natural Resources
LiDAR QA/QC – Did I get what I paid for?
Vertical Accuracy AssessmentValidation Points
Level ground away from breaks in topography Open, visible sky
Five cover classes – 20 points per class (30 preferred) L1O – Open terrain L2T – Tall Grass L3B – Brush L4F – Forested L5U - Urban
04/10/2023 Minnesota Department of Natural Resources
Types of AccuracyFundamental Accuracy = Best Case Scenario
Open terrain tested to 95% accuracy
Supplemental Accuracy Accuracy for Cover Classes other than Open terrain
Consolidated Accuracy All Cover Class Accuracies Combined
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 Minnesota Department of Natural Resources
371.93
LiDAR pointsInterpolated Value372.115
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 Minnesota Department of Natural Resources
Winona County Validation Points
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 MN GIS/LIS Fall Workshops
RMSE CalculationsRMSE(z) = Sqrt(sum(Zdata(i) – ZCheck(i))2 / n)
NSSDA Vertical Accuracy 95% Rate = 1.96 * RMSE2
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 MN GIS/LIS Fall Workshops
--------- Report Summary ---------
Error Mean: -0.116Error Range: [-0.435,0.143]Skew: -0.305RMSE(z): 0.161NMAS/VMAS Accuracy(z) (90% CI): ±0.265ASPRS/NSSDA Accuracy(z) (95% CI): ±0.315
176 control points included in summary out of 176- 0 control points turned off- 0 control points returned no-data
--------- Control Points ---------
Name Control X Control Y Control Z Surface Z Error L1O0 604760.340 4878787.629 201.217 201.389 -0.172 L5U1 608921.294 4878065.350 201.488 201.806 -0.318 L1O2 610991.353 4876621.369 200.214 200.397 -0.183 L1O3 607292.402 4874401.804 233.428 233.606 -0.178 L1O4 622397.772 4873262.387 207.292 207.356 -0.064 L1O5 626922.206 4869248.810 202.936 202.969 -0.033 L1O6 631669.497 4863815.331 200.254 200.333 -0.079 L1O7 635439.901 4857649.190 375.011 375.070 -0.059 L1O8 625518.897 4864620.423 385.756 385.722 0.034 L2T9 621174.012 4864494.226 388.359 388.470 -0.111 L2T10 620283.975 4857065.579 386.810 387.048 -0.238
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 Minnesota Department of Natural Resources
Winona County Validation Report
RMSE across cover Types
RMSE0.000
0.050
0.100
0.150
0.200
0.250
0.127
0.166
0.196
0.172
0.136
0.161
L1OL2TL3BL4FL5UOverall
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 Minnesota Department of Natural Resources
Winona County Validation Report
175 225 275 325 375 425-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
Vertical Error Distribution
L1OL2TL3BL4FL5U
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 MN GIS/LIS Fall Workshops
Then…..If the data does not meet spec Vendor is notified and delivered QA/QC Checklist
Some issues are clear and some are not
If the data is deemed to meet or exceed spec Packaging and Publishing Metadata, Services, etc…..
LiDAR QA/QC – Did I get what I paid for?
04/10/2023 MN GIS/LIS Fall Workshops
National Accuracy Standards Specifications
USGS Base LiDAR Specifications V13
NDEP Guidelines For Digital Elevation Data
LiDAR QA/QC – Did I get what I paid for?