Download - Ortho & LiDAR
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Ortho & LiDARAccuracy Assessment
Mike Tully President & CEO, Aerial Services, Inc.Cedar Falls, Iowa
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FAIL
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FAIL
George Washington Bridge, NY
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FAIL
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FAIL
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Now What?
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Take Away:
Why you should care about positional accuracy!
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“Intended Use”
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What do you mean by “accuracy”?
Accuracy
Precision
Completeness
Currency
Consistency
Others
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Accuracy Defined
Simple & Sweet
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How Tall Are You?
“Measurement Error
is InEscapable
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Measuring Error
Surveyed XYZ
Image XYZ∆Y
∆X
∆R
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Quantifying Error
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Probability & Confidence
Below Mean Above MeanMean
±1 SD68%
±2 SD95%
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NMAS 2’ Contours to NSSDA Standards
Error in Z
-1.2
-1.1
-1.0
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
0
2
4
6
8
10
12 Mean
Freq
uenc
y
NMAS 2’ Contours requires ½ Contour Interval = 1.0’ Accuracy.
NSSDA with 95% Confidence requires 1 RMSE of 0.61’
Observed
Actual Data
95% Confidence
2 SD
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Non-”Normal”
Skewed
“Normal”
“Peakedness”
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Accuracy Standards
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Accuracy StandardsNational
NSSDA
ASPRS
NMAS
Other
FEMA
USGS
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Changing Technology … Evolving Standards
3 inch6 inch1 meterOrthos (GSD)
502…1…Lidar (points/sq m)
TerrestrialMobileAerial
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Next-Gen StandardsASPRS [Draft] Accuracy Standards for Digital Geospatial
Data, 2012
Includes a new high accuracy level “X”
Class Pts/m2 RMSEz
FVA NSSDA
95%
CVA NSSDA
95%
Relative Swath
Overlap RMSDz
IIX 2 12.5 24.5 24.5 9IIA 1 12.5 24.5 36.3 10IIB 0.5 12.5 24.5 49.0 11
Class IIA = USGS minimum vertical accuracy (unclassified lidar)
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Assessing Accuracy
Ortho & Lidar
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Advanced Visual Metrics
Visual inspection of hydro-flattening seems to be predominant quality metric. There are BETTER ways!
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Error Reporting: Lidar & Orthos
Co-Registered LiDAR and Ortho accuracies are reported.
SIS Topo Analyst™
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LiDAR Accuracy Metrics
COVERAGE
OVERLAPS
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Point Density Plots
Water Voids / Holes
LiDAR Accuracy Metrics
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LiDAR Accuracy Metrics
Relative Accuracy (RMSD)
Z-diff Rasters
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Rigorous StatisticsAutomated QA / Verification
LiDAR Accuracy
Metadata Errors
Control Point Errors
Classification Errors
Error Distribution
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How do you know it’s good enough?
When Accuracy Counts
Visual Inspection
3rd Party Expert
Proven Methods / Standards
Verified Results
Intended Use
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