remote sensing lidar & photogrammetry · remote sensing lidar & photogrammetry 19 may 2017....
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REMOTE SENSING LiDAR & PHOTOGRAMMETRY19 May 2017
SERVICES
Visual Inspections
Photo maps
Digital Terrain Models
Thermal Inspections
Aerial Imagery Volume Computations
Aerial Video Training & Consultancy
SYSTEMS
3
MD4-1000
HEF-30 (2x)
Zenith (2 x)
DJI Inspire I (2x)
Asctec Falcon V8 (3x)
Trimble UX 5 HP
Cessna Balloon (5x)
SkeyeBat
CLIENTS
UAV LiDAR vs PHOTOGRAMMETRY
5
🥊🥊
LiDAR PRINCIPLE
6
Distance = Time of travel / 2
Speed of light
Transmitter
Receiver Reflector
BATHYMETRIC LiDAR
7
LiDAR PRINCIPLE ACTIVE LIGHT
8
POSITIONING LIDAR
9
10
POSITIONING LIDAR
11
POSITIONING LIDAR
12
POSITIONING LIDAR
13
POSITIONING LIDAR
POSITION AND ORIENTATION ERRORS
ARE NOT THE SAME FOR ALL
RETURNS
PER SCAN
=> NOT CORRELATED
LiDAR ERROR SOURCES
14
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
LiDAR ERROR SOURCES
15
Range
Between 5 mm to 20 mm
Position
With RTK or PPP Positioning between 15 mm and 50 mm
Orientation
Between 0.025 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 mm2 + 16.5 mm2) = 19.83 mm
Range and Positioning error: 20 mm + 19.83 mm = 39.83 mm
IMU accuracy Pitch and roll: 0.15° ⟹ 60 meters Range = 60 * tan(0.15°) = 15.7 cm
IMU accuracy Pitch and roll: 0.025° ⟹ 60 meters Range = 60 * tan(0.015°) = 2.62 cm
Total Error = √(15.72 + 3.92) = 16.18 cm / Total Error = √(2.622 + 3.92) = 4.7 cm
LiDAR PROJECT SCHEVENINGEN BREAKWATER
PHOTOGRAMMETRY
17
PHOTOGRAMMETRY
18
PHOTOGRAMMETRY
19
PHOTOGRAMMETRY
20
POSITION AND ORIENTATION ERRORS
ARE THE SAME FOR ALL PIXELS
PER PHOTOGRAPH
CORRELATED
NOT WITH ROLLING SHUTTER !!
Rolling Shutter and Photogrammetry
21
STEREO VIEWING
22
PHOTOGRAMMETRY
PHOTOGRAMMETRY
PHOTOGRAMMETRY ALLIGNMENT
PHOTOGRAMMETRY
PHOTOGRAMMETRY
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 = √((1.5 ∗ 0.7)2 + 32) = 3.18 cm
PHOTOGRAMMETRY SAMPLE PROJECT
PHOTOGRAMMETRY SAMPLE PROJECT
PHOTOGRAMMETRY SAMPLE PROJECT
PHOTOGRAMMETRY ACCURACIES BREAKWATER SCHEVENINGEN
X Y
Height
Level GPS DEM Dz-1 Dz-2 Absolute Dz-1 Absolute Dz-2
GCP01 77542.555 457425.012 5.676 5.681 5.686 0.005 0.010 0.005 0.010
GCP02 77519.250 457437.892 5.117 5.117 5.118 0.000 0.001 0.000 0.001
GCP03 77524.464 457471.887 4.607 4.623 4.62 0.016 0.013 0.016 0.013
GCP04 77534.839 457515.828 5.557 5.564 5.564 0.007 0.007 0.007 0.007
GCP07 77482.622 457470.247 4.542 4.544 4.541 0.002 -0.001 0.002 0.001
GCP08 77455.233 457499.366 4.525 4.533 4.523 0.008 -0.002 0.008 0.002
GCP14 77326.597 457699.824 4.519 4.521 4.516 0.002 -0.003 0.002 0.003
GCP20 77285.905 457852.778 4.511 4.509 4.511 -0.002 0.000 0.002 0.000
GCP23 77283.584 457876.050 4.496 4.502 4.494 0.006 -0.002 0.006 0.002
Average 0.005 0.003 0.005 0.004
STDEV 0.005 0.006 0.005 0.005
Dz-1 = Difference Level - GPS
Dz-2 = Difference Level - DEM
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.