Explore the findings of McCain McMurray, Remote Sensing Specialist at NewFields, who surveyed an open pit mine in New Mexico to assess the accuracy of the senseFly eBee mapping UAS (UAV/drone).
2. Overview
- Survey background
- eBee unmanned aircraft system (UAS)
- Survey site and ground control
- Planning the flight
- Flying the survey
- Processing the results
- Results: point cloud, orthomosaic, digital surface model
- Assessing the accuracy of results
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4. eBee UAS
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UAV Technical Specifications
Wingspan 97 cm
Weight 700 g
Payload 16 megapixel camera
Endurance 50 minutes of flight time
Propulsion Electric brushless motor
Nominal cruise speed 55 km/h
Wind resistance Up to 40 km/h
Survey area (4 cm) 1.50 km2
12. Survey results
- Postflight outputs three main survey results: a point cloud, a digital
surface model (DSM) and an orthomosaic
- Point cloud is a set of points plotted in a three dimensional
coordinate system
- DSM is a rasterized interpolation of the point cloud
- An orthomosaic is a composite aerial image that has been
projected on top of the DSM
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13. Survey results: point cloud
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- > 53 million points
- Average point spacing 0.154 m
- Point density 42.375 points/m2
- Colored using RGB data from imagery
14. GSD and RMSE
- “RMSE is the square root of the average of the set of squared
differences between dataset coordinate values and coordinate
values from an independent source of higher accuracy for identical
points.” - ASPRS
- Expected relative accuracy: 1-2 pixels horizontally, 2-3 pixels
vertically
- GSD: 4.33 cm
- 4.33 cm < Expected RMSExy < 8.66 cm
- 8.66 cm < Expected RMSEz < 12.99 cm
- Absolute accuracy is expected to be within these ranges if accurate
GCPs are used to calibrate the survey data
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15. Accuracy assessment: point cloud
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- Point cloud more accurate than
orthomosaic and DSM
- Conducted using Postflight
- Validation GCPs added as
“check points”
- Not incorporated in processing
the survey data
- Postflight automatically
calculates RMSE for x, y and z
- RMSEx = 3.71 cm (= 0.86 * GSD)
- RMSEy = 6.55 cm (= 1.51 * GSD)
- RMSEz = 7.04 cm (= 1.63 * GSD)
19. Accuracy assessment: DSM
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- Validation GCPs located in orthomosaic, elevation of corresponding
cell in DSM entered into Excel to calculate RMSE
- RMSEz = 7.71 cm (= 1.78 * GSD)
21. Conclusion
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This survey and accuracy assessment demonstrate that the eBee UAV
is capable of generating survey datasets with accuracy levels that meet
and exceed the expected relationship with GSD.
Editor's Notes
Name
Title
I’d like to thank Sensefly for giving me this opportunity to present some of the work I’ve been doing with their eBee UAS.
NF is a 300 person environmental consulting firm
I started 9 months ago
- UAS data facilitate the work being done by scientists and engineers?
- Day 1 – figure out how to use the eBee
Survey and acc ass here demonstrates the quality and accuracy of data that can be eBee produces
Define UAS [show equipment]
basic characteristics of the eBee UAV
Incredible wind resistance for the lightweight design – tell story of crabbing
Another cool thing – describe shutting off motor to reduce vibrations during exposure
Software even better – flexible, reliable
Near Deming, NM (SW corner of the state)
Inactive open pit mine on the side of a small hill
Less than ¼ square mile
Pit, cleared gravel area, surrounded by high desert environment
Legal – partnered with NMSU’s Physical Science Laboratory
History working with drones
Several COAs in NM
We contracted them to operate under their COA
Spread homogeneously across the survey site
Higher density near pit/hill
Vertical relief
Spread homogeneously across the survey site
Higher density near pit/hill
Vertical relief
White icons indicate calibration GCPs, those used to calibrate the survey data and tie them to real-world coordinates
Red icons indicate validation GCPs used to assess the accuracy of the survey products.
Search location – Cage, NM
Find survey area
Drag and drop survey boundaries
Place start position of the eBee
Check resolution
Confirm overlap is 60%, 75%
Increase working area radius
Briefly touch on safety feature check boxes
Generate perpendicular flight lines
Use elevation data to set absolute waypoint altitudes
Initially annoyed – only monitoring picture -- looking bored.
However – supports reliability of eBee
Flight log sheet – used to record weather, takeoff/landing, problems, observations
Postflight requires minimum of 3 GCPs to calibrate survey data
5-10 calibration GCPs are typically sufficient
9 calibration GCPs were used for this project
Each GCP should be visible in a minimum of two images
Optimal results: each GCP should be visible in at least 5 images
Processing in Postflight is very straightforward
Number of different options for customizing the data being generated
Default options typically work well
Processing is hands-off
Often leave mine to run over night
This project required about 6 hours total processing – all hands-off
Note that this model includes above-ground features