Mike Zoltek, PLS, CP, CFedS, GISPSenior Project Manager
UAS to Accuracies…how good are they really?
Portsmouth Bypass• Woolpert was contracted to
provide aerial mapping for the ~16-linear-mile Portsmouth Bypass, which is currently being built as part of a $429 million construction project.
• Create a viable and repeatable solution for construction monitoring
Portsmouth Bypass Corridor – Client needs
• Provide data to support the payment of contractor fees based upon cut-fill quantities
• Obtain aerial imagery at 2 cm GSD to provide a cohesive snapshot of site conditions (imagery captured in a single day!)
Portsmouth Bypass Corridor - Deliverables
• LandXML file of 1-foot contours
• 2 cm imagery
Portsmouth Bypass Corridor
Woolpert proposed solution…
Portsmouth Bypass CorridorCollect 2-centimeter GSD aerial imagery...with Woolpert’s Renaissance Surrogate UAS capture system…
Portsmouth Bypass Corridor
Utilize 2 cm GSD imagery to create an auto-correlated point cloud
Portsmouth Bypass CorridorCreate a DSM surface from point cloud
UAS
Portsmouth Bypass CorridorExport point cloud a LAS file of entire project corridor.UAS
Portsmouth Bypass Corridor
Use traditional Lidar processing workflow to create desired deliverable
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RENAISSANCETM What is it?• Combines the benefits of manned
capture and UAS workflows
• Driven by Affordability• Consumer Grade Camera• Single-Engine Aircraft• Pilot-Only Operation• Fly places where UAS can’t (FAA rules)• Computer-Vision Processing (Semi-
automated)
RENAISSANCETM What is it?
Biggest Benefits• Bypass all FAA UAS
restrictions!• Extended flight times
• Self-contained “POD”• Mounted to bottom
of a Cessna 172
Portsmouth Bypass Corridor
Workflow Details
Portsmouth Bypass Corridor
Step 1 -• Define project limits (Cad
files provided by client)• Note: Local coordinate
system 70 foot shift from state plane!
UAS
Portsmouth Bypass Corridor
Step 2 -• Create flight plan to collect
2 cm GSD imagery in project coordinate system
• Export flight plan and shift back to “real world” coordinate system
• Plane navigates with GPS, not the contractor coordinate system!
UAS
Portsmouth Bypass Corridor
Step 3 -• Plan Ground Control Points
required to support accuracy requirements for project (0.20 foot vertical RMSE)
• Plan & Provide data to contractor’s surveyors in project coordinate systems
UAS
Portsmouth Bypass Corridor
Step 4 -• Coordinate with contractor’s surveyor to set targets prior to flight• Make sure they are maintained and ready for flightStep 5 -• Capture the imageryStep 6 -• Process the data in Pix4D & create deliverables
UAS
Portsmouth Bypass Corridor
• Processing in Pix4D…
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Pix4D Processing• Analytical Aerial Triangulation (AT)UAS
Pix4D Processing• Comparison of initial and final adjusted camera positions
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Pix4D Processing• Number of overlapping images covering AOI
• 4+ needed for best solution
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Pix4D ProcessingUAS• Digital Surface Model creation to support ortho-rectification
Pix4D Processing• AT Results – North Block summary
• Observations & Camera calibration results
>13 million 2D Observations
~4 million 3D Observations
Portsmouth Bypass Corridor
What worked…• Flight Planning• Target coordination with the contractor• Imagery Acquisition• Creation of Auto correlated point cloud (LAS files)
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Portsmouth Bypass Corridor• What didn’t work…• Creation of Imagery tiles
• 2 cm tile @ 5,000 x 5,000 pixel tiles (Pix4D limitation)• Equates to 100 meter x 100 meter tiles…that is a lot of tiles!
Portsmouth Bypass Corridor• What didn’t work…
• SOLUTION – decimate imagery to 5cm pixel size• 6.25x file size savings!
Portsmouth Bypass Corridor• What didn’t work…Creation of Autocad LandXML database
• File size - could not be loaded in the field on a survey crew’s laptop
Portsmouth Bypass Corridor• What didn’t work…
• SOLUTION – provide 3 foot grid in ASCII xyz format• Still would not work, single file still too large!
Portsmouth Bypass Corridor
• What didn’t work…• SOLUTION – Break up ASCII files in to maximum
20 mb file size each!• Woolpert “script”
1825131.200 328536.466 542.174
1825134.186 328536.466 542.193
1825137.171 328536.466 542.702
1825125.229 328533.480 542.276
1825128.214 328533.480 541.945
1825131.200 328533.480 542.164
1825134.186 328533.480 541.954
1825137.171 328533.480 542.164
1825119.258 328530.495 541.363
1825122.243 328530.495 541.696
1825125.229 328530.495 541.861
1825128.214 328530.495 541.857
1825131.200 328530.495 541.741
1825134.186 328530.495 542.368
1825137.171 328530.495 542.249
1825140.157 328530.495 542.726
1825110.301 328527.509 540.745
1825113.287 328527.509 540.740
1825116.272 328527.509 541.073
1825119.258 328527.509 541.213
1825122.243 328527.509 541.422
1825125.229 328527.509 541.875
1825128.214 328527.509 541.817
1825131.200 328527.509 541.833
Portsmouth Bypass Corridor – Flight #2
• Adjusted flying plans (fly higher) to capture 5 cm imagery• Less flight lines = more efficient
capture!• Less image processing time =
faster turn-round time
• Added ground control to strengthen AT solution and account for higher flying height
• Limited deliverables to 5 cm image tiles and 20 mb ASCII files of the 3-foot gridded DSM
UAS
Example Images...
Example Point Clouds…
Portsmouth Bypass Corridor – Point Clouds
Portsmouth Bypass Corridor – Point Clouds
Portsmouth Bypass Corridor – Point Clouds
Portsmouth Bypass Corridor – Point Clouds
Portsmouth Bypass Corridor – Point Clouds
Portsmouth Bypass Corridor – Point Clouds
Portsmouth Bypass Corridor
Significant observations…• No other system (other than traditional photogrammetry) could
collect a site of this size and complexity in a single day• Zero impact an active construction site• No other production methodology could provide 2-3 week turn-
around time for all deliverables
Accuracy results
• Independent client checks:
• “The conventional topo matched up well with the Dec flight, +/-0.2ft.”
• “Everyone on our end was pleased with the data provided from the Dec flight.”
• “Tell your crew I appreciate all their work and efforts”
UAS
How did we know this would work?
Dr. Qassim AbdullahSenior Geospatial Scientist and Associate
Woolpert, Inc.
Woolpert’s UAS and Renaissance Program: Products Accuracy
Report
TRB2017 Annual Conference Washington, D.C. January 8, 2017
• County Line Road Corridor:• 1.3 miles in Dayton, OH• 2-cm Orthos / 40 to 700 pts/m2 point clouds
Accuracy Verification: Controls Layout
1.3 m
iles
B C D EF G
How Accurate are the Renaissance-derived Products?
A B C D E F G0 4 6 8 10 21 38
38 34 32 30 28 17 04.47 0.23 0.16 0.18 0.13 0.05 0.051.89 0.26 0.20 0.14 0.14 0.07 0.054.86 0.35 0.26 0.23 0.19 0.08 0.06
13.51 0.54 0.71 0.40 0.35 0.26 0.178.40 0.60 0.45 0.39 0.34 0.14 0.11
26.49 1.05 1.40 0.78 0.69 0.52 0.34
Accuracy Term
Horizontal Accuracy at 95% (ft.)Vertical Accuracy at 95% (ft.)
RMSE Elev. (ft.)
Processing Scenario
Number of Control PointsNumber of Check Points
RMSE E (ft.)RMSE N (ft.)
Radial RMSE N,E (ft.)HorizontalVertical
The winner: Pair of GCPs every 500 to 700 ft.
along the route…similar to MMS!
name # GCPs RMSE (z) @ GCP
Std Dev (z) @ GCP
RMSE (z) @ QC
Std Dev (z) @ QC
“B” 0 n/a n/a 13.61 ft 2.14 ft
name # GCPs RMSE (z) @ GCP
Std Dev (z) @ GCP
RMSE (z) @ QC
Std Dev (z) @ QC
“C” 4 0.01 ft 0.01 ft 0.58 ft 0.58 ft
name # GCPs RMSE (z) @ GCP
Std Dev (z) @ GCP
RMSE (z) @ QC
Std Dev (z) @ QC
“D” 6 0.02 ft 0.02 ft 0.76 ft 0.75 ft
name # GCPs RMSE (z) @ GCP
Std Dev (z) @ GCP
RMSE (z) @ QC
Std Dev (z) @ QC
“E” 8 0.02 ft 0.02 ft 0.44 ft 0.44 ft
name # GCPs RMSE (z) @ GCP
Std Dev (z) @ GCP
RMSE (z) @ QC
Std Dev (z) @ QC
“F” 10 0.04 ft 0.03 ft 0.47 ft 0.46 ft
name # GCPs RMSE (z) @ GCP
Std Dev (z) @ GCP
RMSE (z) @ QC
Std Dev (z) @ QC
“A” 38 0.13 ft 0.12 ft n/a n/a
Pix4D Processing• AT Results – North Block summary
• Observations & Camera calibration results
Pix4D Processing• AT Results – Run A - no GCPs Held
• Observations & Camera calibration results
Pix4D Processing• AT Results – Run F – all GCPs Held
• Observations & Camera calibration results
Pix4D ProcessingComparison to a metric camera:
4 years between RCD30 (Digital Camera) USGS calibrations = only 2-3 microns difference in focal length!
Takeaways…
• UAS Camera systems are not as “metric” (a.k.a. Stable) as traditional photogrammetric cameras
• Software (e.g. self-cal) can only do so much to compensate for the instability of a camera system
• The variation of self-cal computed focal lengths would indicate there is instability in the camera itself
Takeaways…
• The software appears to be putting the “error budget” in the focal legth
• The variation indicates that the errors may be non-normalized• You cannot use a random point sampling to
accurately asses the accuracy of your data (e.g. Traditional NSSDA 95% accuracy assessment methodology)
However…• UAS products (e.g. auto-correlated point clouds) can support
many needs for high resolution imagery
• Auto-correlated point cloud derivative products can meet many horizontal accuracy requirements for planimetric feature locations
• Auto-correlated point cloud derivative products do not meetmost 3D (a.k.a. vertical) most design grade mapping needs
• Auto correlated point cloud solutions appear to achieve • 2-3 pixel RMSE horizontal accuracies • 4-8 pixel RMSE vertical accuracies
• (Vertical RMSE errors can be larger than ½ foot with 2 cm GSD imagery)
Topics for further discussion…
• When does using a UAS make sense?• How to properly set customer expectations• Where can you fly (FAA restrictions)• Insurance requirements - Liability issues!• Training – FAA Certifications
UAS
Thank you!
Questions?