Relative and absolute calibration of a multihead camera system with oblique and nadir looking cameras for a UAS

Transcription

1 Relative and absolute calibration of a multihead camera system with oblique and nadir looking cameras for a UAS Dipl.-Ing. Frank Niemeyer Rostock University Chair for Geodesy and Geoinformatics UAV-g 2013, 4.-6.Sept.2013, Rostock University

2 Agenda Motivation / Introduction Examples of oblique looking camera systems Four Vision camera system Calibration of each camera Determination of relative orientations between cameras Conclusion UAV-g 2013, 4.-6.Sept.2013, Rostock University 2

3 Four Vision -Camera System Concept UAS Field of View Ground coverage Resulting images and overlapping areas UAV-g 2013, 4.-6.Sept.2013, Rostock University 3

4 Motivation Oblique Looking Cameras Aerial survey with strongly overlapping images from different perspectives Endlap approx. 70 % Side lap approx. 60 % Redundant images support the image block as well as the geo referencing Redundant images allow for an empiric averaging of the BRDF UAV-g 2013, 4.-6.Sept.2013, Rostock University 4

5 BRDF-Measurement Anisotropic Reflection of Bare Soil Channel: Green UAV-g 2013, 4.-6.Sept.2013, Rostock University 5

6 Oblique Multi head systems I Pictometry, MIDAS, Penta-DigiCAM - simple systems with 5 cameras (4 oblique, 1 NADIR) Penta-DigiCAM Malteser Kreuz Bildkonfiguration System MIDAS Track Air UAV-g 2013, 4.-6.Sept.2013, Rostock University 6

7 Oblique Multi head systems II Complex rotating systems with one or 3 medium format cameras Azicam Rolleimetric AOS UAV-g 2013, 4.-6.Sept.2013, Rostock University 7

8 Four Vision Camera System 1st edition Very light Upper part fixedly connected with UAV (computer, converter) Lower part Camera holder Variable pivot mechanism between upper and lower part UAV-g 2013, 4.-6.Sept.2013, Rostock University 8

9 Four Vision Camera System 2nd edition UAV-g 2013, 4.-6.Sept.2013, Rostock University 9

10 Components KTA55 / pitx Board 1.0 GHz dual core T40N 6 * USB x SATA 2 GByte DDR2-RAM power consumption 5 W 120GByte SATA SSD DCDC power converter (22V 5V) Controller for synchronous triggering image of all cameras UAV-g 2013, 4.-6.Sept.2013, Rostock University 10

11 Cameras and lens USB-Boardcamera (Crevis USB 2.0) Sony CCD (½ inch) Pixelsize 4,65 µm 15 frames per second Color version dimensions: 29x29x29 mm weight: 38 g Power consumption 2.5 W 1280 x 1024 Pixel lenses Fujinon C-Mount 9 mm Focal length (oblique) 6 mm Focal length (Nadir) weight: 45 g SDK and Halcon driver available UAV-g 2013, 4.-6.Sept.2013, Rostock University 11

12 Camera Calibration with Australis Test stand Representation of all camera positions and the visual connections to the target Overview of the layout of all targets UAV-g 2013, 4.-6.Sept.2013, Rostock University 12

13 Australis Conditions Illuminated retroreflective targets with additional LED at Camera system Number of cameras positions : 18 Number of images per view : 5 Number of images : 90 Number of mapped and reconstructed targets: 56 Conditions of Australis Geometric arrangement of the marks shall not change Originally designed for close range photogrammetry Y-axis = line of sight Mind. 5 stamps must be detected in single images At least 6-8 marks per image for Camera calibration Use of portrait and landscape-format images (4.5 x 4.5 cm²) UAV-g 2013, 4.-6.Sept.2013, Rostock University 13

14 Four Vision - Camera Calibration Interior Orientation Principal point: One lens mounted on different cameras Radial distortion: five lenses mounted on one camera CCD-chips are manufactured differently ( x,y max = 368 µm) Lenses are manufactured with high precision UAV-g 2013, 4.-6.Sept.2013, Rostock University 14

15 Coordinate Systems Coordinate system: Australis (Y-axis = line of sight) Coordinate system during the flight (Z-axis = line of sight) UAV-g 2013, 4.-6.Sept.2013, Rostock University 15

16 Results Before Flight ( ) Exterior orientation parameters of the oblique-looking cameras in the coordinate system of Australis (Schima,2013) Camera X [mm] Y [mm] Z [mm] Azimut[ ] Elevation[ ] Roll[ ] MV-CS27U (±0.13) (±0.09) (±0.12) 2.20 (±0.05) (±0.01) 2.11 (±0.04) MV-CS27U (±0.14) (±0.09) (±0.12) (±0.02) 0.07 (±0.03) (±0.01) MV-CS27U (±0.15) (±0.12) (±0.14) (±0.03) (±0.02) (±0.02) MV-CS27U (±0.15) (±0.15) (±0.18) (±0.02) 0.20 (±0.04) (±0.01) Orientation during the flight MV-CS27U 1 MV-CS27U 2 MV-CS27U 3 MV-CS27U 4 MV-CS27U 5 Azimut [ ] Elevation [ ] Roll [ ] Focus for close range (4 m) F-Stop Number 4 Determination of values with a very high accuracy Position max : ±0.18mm, Orientation max : ±0.05 UAV-g 2013, 4.-6.Sept.2013, Rostock University 16

17 First flight success ( ) Test field Rostock 121 Image Sequences 45 m high Manual flight mode Computed with Photoscan from AgiSoft UAV-g 2013, 4.-6.Sept.2013, Rostock University 17

18 Results After Flight ( ) Camera X [mm] Y [mm] Z [mm] Azimut[ ] Elevation[ ] Roll[ ] MV-CS27U 1 Differenz (±0.15) (±0.18) (±0.28) (±0.03) (±0.01) (±0.01) MV-CS27U 2 Differenz (±0.20) (±0.15) (±0.14) (±0.01) (±0.01) (±0.01) MV-CS27U 3 Differenz 1.96 (±0.16) (±0.16) (±0.15) (±0.01) (±0.01) (±0.01) MV-CS27U 5 Differenz (±0.16) (±0.15) (±0.15) (±0.01) (±0.01) (±0.01) 0.16 Focus for altitude of 45 m F-Stop Number 4 Determination of values with a very high accuracy Position max : ±0.28mm, Orientation max : ±0.03 Differences between before and after flight Position max : 2.21mm, Orientation max : CBA - Workshop und 2. UAS Workshop, Mai 2013, Beuth Hochschule für Technik Berlin 18

19 Conclusion Australis is a very powerful methode for: Camera calibration Determination of relativ orientations between different cameras in one camera system methode requires also a comparatively low experimental and temporal effort cameras are different and need to be calibrated for each lenses are manufactured with high precision Accuracy of relativ orientation depends on systematic influences like: Focusing Altitude F-stop parameters of the relative orientation are good approximations for further calculations or restrictions in bundle block adjustment 19. CBA - Workshop und 2. UAS Workshop, Mai 2013, Beuth Hochschule für Technik Berlin 19

20 References Grenzdörffer, G., Niemeyer, F., Schmidt, F.: Development of Four Vision Camera System for a Micro-UAV. In: Shortis, M., El-Sheimy, N. (Ed.): International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, XXII ISPRS Congress Melbourne. Volume XXXIX-B1. Copernicus Publications, ISBN: , S Schima, R. (2013): Bestimmung der inneren und relativen Orientierung einschließlich der Systemstabilität für das Kamerasystem Four Vision Entwicklung eines Versuchsaufbaus und Erprobung einer Kalibriermethode für ein Mehrkamerasystem zur Luftbildphotogrammetrie mithilfe der Software Australis. wissenschaftliche Begleitarbeit im Projekt PFIFFikus, Universität Rostock, Rostock. 19. CBA - Workshop und 2. UAS Workshop, Mai 2013, Beuth Hochschule für Technik Berlin 20

21 Thanks for your attention! UAV-g 2013, 4.-6.Sept.2013, Rostock University 21