Ortho & LiDARAccuracy Assessment

Mike Tully President & CEO, Aerial Services, Inc.Cedar Falls, Iowa

FAIL

FAIL

George Washington Bridge, NY

FAIL

FAIL

Now What?

Take Away:

Why you should care about positional accuracy!

“Intended Use”

What do you mean by “accuracy”?

Accuracy

Precision

Completeness

Currency

Consistency

Others

Accuracy Defined

Simple & Sweet

How Tall Are You?

“Measurement Error

is InEscapable

Measuring Error

Surveyed XYZ

Image XYZ∆Y

∆X

∆R

Quantifying Error

Probability & Confidence

Below Mean Above MeanMean

±1 SD68%

±2 SD95%

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

Non-”Normal”

Skewed

“Normal”

“Peakedness”

Accuracy Standards

Accuracy StandardsNational

NSSDA

ASPRS

NMAS

Other

FEMA

USGS

Changing Technology … Evolving Standards

3 inch6 inch1 meterOrthos (GSD)

502…1…Lidar (points/sq m)

TerrestrialMobileAerial

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)

Assessing Accuracy

Ortho & Lidar

Advanced Visual Metrics

Visual inspection of hydro-flattening seems to be predominant quality metric. There are BETTER ways!

Error Reporting: Lidar & Orthos

Co-Registered LiDAR and Ortho accuracies are reported.

SIS Topo Analyst™

LiDAR Accuracy Metrics

COVERAGE

OVERLAPS

Point Density Plots

Water Voids / Holes

LiDAR Accuracy Metrics

LiDAR Accuracy Metrics

Relative Accuracy (RMSD)

Z-diff Rasters

Rigorous StatisticsAutomated QA / Verification

LiDAR Accuracy

Metadata Errors

Control Point Errors

Classification Errors

Error Distribution

How do you know it’s good enough?

When Accuracy Counts

Visual Inspection

3rd Party Expert

Proven Methods / Standards

Verified Results

Intended Use