1.
Accuracy Assessment of an eBee UAS Survey
McCain McMurray
Remote Sensing Specialist

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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3.
Background
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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

5.
Survey site
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6.
Ground control
- Surveyors contracted to create 20 GCPs prior to survey
- RTK GNSS, 2 – 3 cm precision
- 5 gallon bucket lids used for photogrammetric targets
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7.
Ground Control
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8.
Mission planning in eMotion 2 (senseFly)
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9.
Flying the survey
- 38 minute flight
- 412 images captured
- Avg. wind speed 7.5 km/h, max. wind speed 12.2 km/h
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10.
Adding calibration GCPs in Postflight Terra 3D
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11.
Processing the survey data
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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)

16.
Survey results: orthomosaic
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17.
Accuracy assessment: orthomosaic
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- Location of validation GCPs in orthomosaic measured in ArcMap
and entered into Excel to calculate RMSE
- RMSEx = 4.02 cm (= 0.93 * GSD)
- RMSEy = 7.89 cm (= 1.82 * GSD)

18.
Survey results: DSM
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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)

20.
Accuracy assessment: summary
- Expected accuracy for survey products:
RMSExy = GSD * 1.5
RMSEz = GSD * 2.5
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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.