utilizing unmanned aircraft system (uas) technology without the need for ground control points mike...

Utilizing Unmanned Aircraft System (UAS) Technology without the need for Ground Control Points

Mike Gilkey and Tom Hughes

3DAerial Solutions LLC

2015 Ohio GIS ConferenceSeptember 21 - 23, 2015 | Hyatt Regency Columbus| Columbus, Ohio

Overview• UAS technology effectively complements existing techniques,

fitting between large-area satellite/manned aircraft imagery and smaller coverage, time-consuming, but highly accurate terrestrial approaches

• The standard senseFly eBee can achieve 3 cm Orthomosaic (horizontal) and 5 cm Digital Elevation Model (vertical) accuracy. This provides an expected level of accuracy of between 1-3x Ground Sample Distance (GSD), but requires use of Ground Control Points (GCPs)

• The senseFly eBee RTK can achieve 3 cm horizontal and 5 cm vertical accuracy with an expected level of accuracy of between 1-3x GSD without using GCPs

9/22/15Ohio GIS Conference

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3D Aerial Solutions•3D Aerial is an Unmanned Aircraft System (UAS)

technology company▫Based in Dayton, OH.

•We provide commercial UAS flying services with the eBee. ▫Received FAA Section 333 exemption and blanket COA in

March 2015▫FAA aircraft registration complete in May 2015▫Over 150 flights, > 37 flight hours since June

•We also provide UAS consulting services and are a sales representative for senseFly products.


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senseFly eBee• eBee

~1.5 pound take off weight38 inch wingspanEPP foam and composite construction160 W brushless DC motor~50 minutes of flight25-56 mph cruise speedoperates in winds up to 28 mphRadio link to 1.8 milesSony WX 18.2 MP camera (others available)GSD: down to 0.6 inchDEM accuracy: ~1-3x GSD (with GCP)Accuracy (with GCP): 1.2 in (hort), 2.0 in (vert)Accuracy (no GCP): 3.3-16.4 ft (hort & vert)


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senseFly eBee RTK (Real Time Kinematic)• eBee

~1.6 pound take off weight38 inch wingspanEPP foam and composite construction160 W brushless DC motor~40 minutes of flight25-56 mph cruise speedoperates in winds up to 28 mphRadio link to 1.8 milesSony WX 18.2 MP camera (others available)L1/L2, GPS & GLONAS RTK receiverGSD: down to 0.6 inchDEM accuracy: ~1-3x GSDAccuracy (no GCP): 1.2 in (hort), 2.0 in (vert)


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Bundled Software•The eBee comes with the following software

▫eMotion 2: Flight planning and control application for precision image collection Produces geotagged images with selected resolution and overlap to

support desired GIS products▫Postflight Terra 3D (Pix4D Product): Photogrammetry

application to create 2-D orthomosaics and 3-D DSM Outputs are compatible with most major GIS packages including erdas,

ArcGIS, Global Mapper and Quantum GIS

•There are no additional subscription fees with either package and software updates are provided for the life of the product.


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Postflight Terra 3D


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Postflight Terra 3D


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Process Flow

GenerateProducts

Pre-MissionPlanning

Pre-FlightChecklist

FlyMission

Post FlightChecklist

DataMerge

DataProcessing

3 Methods to use eBee RTK• Virtual Reference Station (Base Station not required)

▫ Create DSMs and orthomosaics using reference station networks to achieve highly accurate absolute geotags.

▫ Useful when you want to benefit from the high absolute accuracy achievable using an Ntrip networks, or when surveying equipment is unavailable or inconvenient.

• Unknown point (Post process)▫ Geotag relative to an approximate base station position, then post-process GNSS

data to reach high absolute coordinate accuracy. ▫ Useful for green-field surveying when no GCPs have been set, when in-field time is

limited, or it is impractical to survey beforehand. • Known point (Use base station)

▫ Obtain high absolute coordinate accuracy using your precisely measured base station position as a GCP.

▫ Useful when a survey has already been completed and reference points are already marked out. No post-processing is needed to achieve RTK-level geotag accuracy.


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A study of point cloud accuracy

•Two experiments were conducted


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Flight One Flight 2

Assess maximum accuracy of eBee RTK

Assess impact of adverse lighting and weather on accuracy

RTK using VRS RTK using VRS

Area: 49.4 acres Area: 49.4 acres

GSD: .98 inch GSD: .98 inch

Imaging altitude: 266 ft Imaging altitude: 531 ft

Overlap: 80% Overlap: 80%

Perpendicular flights No perpendicular flights

Bright sunny day Cloudy (low light) and windy (20 mph)

Accuracy Measurements

•Accuracy was calculated using Root Mean Square Error


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n is the number of pointsXdata is the X coordinate of the datasetXcheck is the X coordinate of a reference point

Results9/22/15Ohio GIS Conference

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Verification Points in the Point Cloud

Orthomosaic and DSM Accuracy

Conclusions: With high overlap and high resolution (2.5cm), we can see that, in these ideal lighting and weather condition, the 3Bee RTK can achieve a very high level of accuracy, both horizontally (2.6cm) and vertically (3.1cm)

Conclusions: As both the DSM and orthomosaic are based on the point cloud, the final accuracy is clearly slightly lower, horizontally (3.3cm) and vertically (3.5cm)

X(m) Y(m) Z(m)

Mean Error 0.008 0.001 -0.023

Standard Deviation 0.019 0.015 0.021

RMSE 0.020 0.015 0.031

RMSE XY 0.026

X(m) Y(m) Z(m)

Mean Error 0.002 -0.005 -0.023


RMSE 0.023 0.023 0.035

RMSE XY 0.033

Results continued9/22/15Ohio GIS Conference

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Inaccurate Geotags

Low light, windy conditions

Conclusions: Even with inaccurate geotags in 10% of the images, the accuracy of the entire dataset is maintained, thanks to the capabilities of Postflight Terra 3D

Conclusions: Flights over the same zone during windy and low light level conditions demonstrated that the eBee RTK has no difficulty achieving one to three times GSD accuracy, in line with senseFly’s claims

X(m) Y(m) Z(m)

Mean Error 0.015 -0.001 -0.046


RMSE 0.023 0.015 0.048

RMSE XY 0.028

X(m) Y(m) Z(m)

Mean Error -0.045 -0.069 -0.049


RMSE 0.049 0.075 0.07

RMSE XY 0.028

Conclusions

•The eBee RTK offers a convenient and efficient method to to create accurate DSM without the need for ground control points

•Under ideal conditions, accuracy of 2.6 cm horizontally and 3.1 cm vertically was obtained

•Performance degrades gracefully under deteriorated environmental conditions, with demonstrated accuracy of 8.9 cm horizontally and 7 cm vertically.


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References

•eBee RTK Accuracy Assessment A. Roze1, J-C. Zufferey2, A. Beyeler3, A. McClellan4

1 Application Engineer, senseFly, 2 CEO, senseFly, 3 CTO, senseFly, 4 Technical Writer, senseFly

•eBee RTK Extended Users Manual, Revision 1 / September 2014, senseFly Ltd.


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Backup


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Virtual Reference System (VRS)

•VRS is a system of hardware and software designed to facilitate real-time GPS/GNSS positioning based on a set of reference stations

•Ohio Dept Of Transportation (ODOT) utilizes its CORS (Continuously Operating Reference Station) network (Trimble) to perform the role of the reference stations

•Eliminates the need for a separate base station


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ODOT VRS RTK Network


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utilizing unmanned aircraft system (uas) technology without the need for ground control points mike...

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