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Creating DEM using a mini-UAS
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  • 1. Creating digital terrain models using amini-UAS: methods and applications Dr David Gillieson SkyView Solutions Pty Ltd PO Box 158 Atherton, Q 4883 www.skyviewsolutions.com.au
  • 2. What is an UAS?• Unmanned aerial system – Remotely controlled airframe with autopilot and payload (eg. drone) – Remotely piloted aircraft with ground control station• Many types (micro-, small, medium, large; planes, helicopters; electric, petrol motors)• Initially developed by Defence aerospace industries, but now well established in civilian operations and more accessible
  • 3. Types of UAVPredator Heron Bat Zephyr
  • 4. Unmanned Airborne Systems (UAS)Orthophoto mosaic from one flight (55ha) Swinglet UAS
  • 5. 3D imaging from stereo UAS photography • Uses bundle block adjustment approach • Prepare geotagged images with significant stereo overlap • Relate image matchpoints to camera photogrammetry • Create stereo model with accurate depth measurements
  • 6. Point cloud from UAS photography PO Box 158 Atherton, Q 4883 www.skyviewsolutions.com.au
  • 7. Triangular mesh surface (TIN) PO Box 158 Atherton, Q 4883 www.skyviewsolutions.com.au
  • 8. Creating DEMs from UAS photography – example from FNQ• Three flights conducted at 120m AGL• Photos geotagged and telemetry data created including heading, GPS altitude, pitch, roll and yaw data• Data used on a local computer to generate a coarse mesh DTM and 50cm pixel orthophoto mosaic for evaluation• Geotagged photos and telemetry data uploaded to a cloud computer at the Swiss Technical University in Lausanne for final processing• Products generated included an orthophoto mosaic with 5cm pixels, an orthoDTM, ASCII point file, camera parameters report and accuracy report
  • 9. Bundle block adjustment• The software searches for matching points between image pairs by analyzing all uploaded images (~230)• Those matching points are used in a bundle block adjustment to reconstruct the exact position and orientation of the airborne camera for every acquired image• Based on this reconstruction the matching points are verified and their 3D coordinates are calculated from the UAS telemetry data• Those 3D points are interpolated to form a triangulated irregular network (TIN)
  • 10. • Connectivity graphic showing quality and number of image keypoint matches. Total of 232 images used in analysis
  • 11. Orthorectified image mosaic
  • 12. Bundle block adjustment StatisticsFeaturetotal number of keypoint observations 1,104,692total number of 3D points 440,908mean re-projection error 0.793865 pixels (= 4cm)
  • 13. Hillshaded OrthoDTM
  • 14. Accuracy assessment• Thirty correlation points on grid established with RTK GPS• Marker plates visible in UAS orthophoto mosaic• Extract height values from DTM – average value from 1m buffer around points• Linear regression between RTK and DTM values• Thanks to Brendan Twine of Twine Surveys, Atherton
  • 15. Comparison between elevations from the DTM and surveyed elevations 550 y = 1.0093x - 13.039 R2 = 0.9833 545 540 535elevation from RTK 530 525 520 515 510 520.00 525.00 530.00 535.00 540.00 545.00 550.00 555.00 560.00 elevation from DEM
  • 16. One metre contours
  • 17. Half metre contours
  • 18. Water flow direction
  • 19. Water flow accumulation
  • 20. Conclusions• Mini-UAS can be used to generate high quality orthophoto mosaics and digital terrain models of small areas up to 100ha• These can be captured in overcast conditions as long as wind speed <10knots• DTMs correlate well with RTK GPS surveys, and have comparable resolution to LIDAR• DTMs can be used for hydrological modelling