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?