REMOTE SENSING LiDAR & PHOTOGRAMMETRY 19 May 2017

Transcription

1 REMOTE SENSING LiDAR & PHOTOGRAMMETRY 19 May 2017

2 SERVICES Visual Inspections Digital Terrain Models Aerial Imagery Volume Computations Thermal Inspections Photo maps Aerial Video Training & Consultancy

3 SYSTEMS Zenith (2 x) Asctec Falcon V8 (3x) SkeyeBat MD DJI Inspire I (2x) Trimble UX 5 HP HEF-30 (2x) Cessna Balloon (5x) 3

4 CLIENTS

5 UAV LiDAR vs PHOTOGRAMMETRY 5

6 LiDAR PRINCIPLE Transmitter Distance = Time of travel / 2 Speed of light Receiver Reflector 6

7 BATHYMETRIC LiDAR 7

8 LiDAR PRINCIPLE ACTIVE LIGHT 8

9 POSITIONING LIDAR 9

10 POSITIONING LIDAR 10

11 POSITIONING LIDAR 11

12 POSITIONING LIDAR 12

13 POSITIONING LIDAR POSITION AND ORIENTATION ERRORS ARE NOT THE SAME FOR ALL RETURNS PER SCAN => NOT CORRELATED 13

14 LiDAR ERROR SOURCES Sensor Position GPS error INS/IMU error GPS-IMU Integration error Angular Errors Misalignment between LiDAR scanner and IMU (Boresight calibration) Lever arm Error Incorrect positioning between GPS antenna and LiDAR sensor LiDAR Range Error Precision of LiDAR scanner Divergence of Laser beam Multipath error Reflection on a sloping surface 14

15 LiDAR ERROR SOURCES Range Between 5 mm to 20 mm Position With RTK or PPP Positioning between 15 mm and 50 mm Orientation Between degrees and 0.15 degrees Example Sum of all errors Velodyne HDL 32E Scanner Flying Height 60 meters AGL (Above Ground Level) Range error: <= 20 mm GNSS Positioning Horizontal: 1 cm + 1ppm, assume 11mm Vertical : 1.5 times horizontal = 16.5 mm Total = (11 mm mm 2) = mm Range and Positioning error: 20 mm mm = mm IMU accuracy Pitch and roll: meters Range = 60 * tan(0.15 ) = 15.7 cm IMU accuracy Pitch and roll: meters Range = 60 * tan(0.015 ) = 2.62 cm Total Error = ( ) = cm / Total Error = ( ) = 4.7 cm 15

16 LiDAR PROJECT SCHEVENINGEN BREAKWATER

17 PHOTOGRAMMETRY 17

18 PHOTOGRAMMETRY 18

19 PHOTOGRAMMETRY 19

20 PHOTOGRAMMETRY POSITION AND ORIENTATION ERRORS ARE THE SAME FOR ALL PIXELS PER PHOTOGRAPH CORRELATED NOT WITH ROLLING SHUTTER!! 20

21 Rolling Shutter and Photogrammetry 21

22 STEREO VIEWING 22

23 PHOTOGRAMMETRY

24 PHOTOGRAMMETRY

25 PHOTOGRAMMETRY ALLIGNMENT

26 PHOTOGRAMMETRY

27 PHOTOGRAMMETRY

28 PHOTOGRAMMETRY ACCURACIES General rules of thumb for photogrammetry with dense matching techniques - Relative accuracy is influenced by resolution (GSD, Ground Sampling Distance) - Absolute accuracy is influenced by quality of the geodetic network (i.e. ground control points) - Absolute accuracy is influenced by the data processing methodology - If all of the above are favorable: - X,Y accuracy is 1 to 1.5 times the GSD - Z accuracy is 1.5 to 2 times the GSD - Absolute accuracy is the quality of the network + relative accuracy Sample project Scheveningen breakwater - Flight altitude 40 meters with Sony A7r (36 Mp and 35mm lens) => GSD = 0.7 cm - Quality of the Ground control points assumed at 2cm X,Y and 3 cm Z - A priori estimated error = (( ) ) = 3.18 cm

29 PHOTOGRAMMETRY SAMPLE PROJECT

30 PHOTOGRAMMETRY SAMPLE PROJECT

31 PHOTOGRAMMETRY SAMPLE PROJECT

32 PHOTOGRAMMETRY ACCURACIES BREAKWATER SCHEVENINGEN X Y Height Level GPS DEM Dz-1 Dz-2 Absolute Dz-1 Absolute Dz-2 GCP01 GCP02 GCP03 GCP04 GCP07 GCP08 GCP14 GCP20 GCP Average STDEV Dz-1 = Difference Level - GPS Dz-2 = Difference Level - DEM

33 LiDAR vs PHOTOGRAMMETRY (UAV ONLY!) LiDAR Vegetation Penetration Detect smaller features (i.e. power line) Quicker data processing No (or little) Ground control Active light (better in dark/shadow areas) No Picture Accuracy Cost Weight (i.e. safety) Photogrammetry Accuracy Costs Weight Picture Only map what you see Longer Processing times Cannot detect small features Ground Control (even with RTK or PPK!) Less accurate in shadow areas CONCLUSION: One sensor is not better than the other. Depends very much on the type of project.

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