Universität Hannover Institut für Photogrammetrie und GeoInformation Issues and Method for...
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Universität Hannover Institut für Photogrammetrie und GeoInformation
Issues and Method for In-Flight and On-Orbit Calibration (only geometry)
Karsten Jacobsen
Institute of Photogrammetry and GeoInformation
University of Hannover
Universität Hannover Institut für Photogrammetrie und GeoInformation
Camera Calibration
Reconstruction of the bundle of rays from the projection center to the object based on measured image positions
Inner orientation of sensor
Exterior orientation = location of projection center + attitude information
System calibration = inner orientation + relation to positional sensors
Universität Hannover Institut für Photogrammetrie und GeoInformation
Inner Orientation
photographic camera – fiducial marks
digital array camera – principal point F(line, sample)
CCD-line sensors
Inner orientation only for 1 CCD-
line
‘
Universität Hannover Institut für Photogrammetrie und GeoInformation
Deformation of the bundle of rays - “systematic image errors“
deformation of bundle of rays causing “systematic image errors“ = effect in images
“systematic image errors OEEPE test block “direct sensor orientation“
averaged image company 2 company 1 coordinate residuals (66 images, 1484 image points)
image
deformed bundle of rays
Universität Hannover Institut für Photogrammetrie und GeoInformation
Self calibration by additional parameters
Set of additional unknowns for fitting systematic errors
Additional parameters from Gotthard / Ebner
optimal if image points located in Gruber points – only mathematic interpretation
Universität Hannover Institut für Photogrammetrie und GeoInformation
Additional parameters Jacobsen (program system BLUH)
angular affinity affinity mathematic justification
mathematic tangential distortion radial symmetric distortion
radial sym. mathematic
1 2 3 4 5
6 7 8 9 10
11 12 mixture between physical and mathematical justification – parameters less correlated like with Ebner set if image points randomly distributed
Universität Hannover Institut für Photogrammetrie und GeoInformation
radial symmetric additional parameters
Often used: r = K1* r3 + K2* r5 + K3* r7
disadvantage: highly correlated, K2 and K3 effective only in corner
Program system BLUH:
r = P9* (r3 – A*r) + P10*r*sin(r*A/(2) + P11*r*sin(r*A/(4)
9 10 11
9 - -0.36 0.24
10 - -0.32
correlation matrix
same data set: correlation K1 – K2 = 0.94
only K1 P9 – P11
Universität Hannover Institut für Photogrammetrie und GeoInformation
in-flight calibration of photographic aerial cameras
Bundle adjustment with self-calibration by additional parameters
- based on the over-determination of the bundle adjustment + control point information
1. Standard block configuration – only parallel flight lines: affinity parameters depending upon control points, other just by over-determination
2. Crossing flight lines – also affinity parameters just by over-determination
OEEPE test block “direct sensor orientation”,
image scale 1 : 5000, 1 : 10 000
Universität Hannover Institut für Photogrammetrie und GeoInformation
determination of focal length and principal point
hg1 – Z1
hg2 – Z2
control points
GPS-SHIFT STANDARD DEVIATION X Y Z SX SY SZ GPS DATA FOR DATA SET 1 .010 -.113 -.278 .008 .008 .004 GPS DATA FOR DATA SET 2 -.069 .124 -.460 .014 .015 .006
CHANGE OF FOCAL LENGTH .039 = CORR. FOR F -> 153.383 GPS-SHIFT ABSOLUT -.094
under standard conditions of aerial images determination of focal length not possible – strong correlation Zo – focal length
Z of projection centers required – possible by GPS, but problems with GPS datum shift, no separation of GPS datum and focal length
- 2 different flying height levels required (like in OEEPE test block)
Universität Hannover Institut für Photogrammetrie und GeoInformation
Digital aerial array cameras
No problems with film deformation, CCD-array usually perfect flat, main problem caused by optics + affinity of CCD (will never change)
“systematic image errors” of synthetic ZI-DMC images (flight over test area) – small affinity deformation, has been confirmed by following laboratory calibration
- original distortion of 4 single optics always respected
“systematic image errors” of CCD-array camera Rollei Q16
typical strong radial symmetric distortion of off-the-shelf optics
Universität Hannover Institut für Photogrammetrie und GeoInformation
Digital aerial array cameras
“systematic image” errors of the ThermScan camera – tangential distortion
wide angle optics normal angle optics – largest vector 1.7 pixels
If optics are exchanged, focal length and principal points have to be calibrated again
focus has to be fixed, after change of focus and going back, not same inner orientation
calibration of zoom-lenses not possible, inner optical system has no sufficient stability, may change after shaking the camera
Universität Hannover Institut für Photogrammetrie und GeoInformation
line scan cameras
HRSC CCD-line camera linearity of CCD-line by laboratory calibration
can also be calibrated under flight conditions, higher number of control points or crossing flight lines required
real problem: boresight
Universität Hannover Institut für Photogrammetrie und GeoInformation
CCD-line camerasIRS-1C
Pan-camera
3 combined CCD-lines
available configuration for calibration determined geometry
most CCD-line cameras used in space equipped with a combination of shorter CCD-lines, calibration under flight conditions required, with combination of images taken from different orbits reduction of required number of control points
Universität Hannover Institut für Photogrammetrie und GeoInformation
“level 1A” space images
QuickBird SPOT ASTER
“systematic image errors” of the orientation of level 1A space images
- no calibration, dominated by exterior orientation
- in general sub-pixel accuracy possible
Universität Hannover Institut für Photogrammetrie und GeoInformation
conclusion
Perspective aerial cameras can and should be calibrated under flight conditions by bundle block adjustment with self-calibration by additional parameters – optimal set of parameters should be used, statistical analysis of parameters required
Stability of film-camera calibration limited, only parts stable over time
focal length and principal point can only be determined by 2 different flying heights + GPS-projection center coordinates
Digital CCD-array cameras mainly influenced by optical distortion
CCD-line cameras used in space usually do use a combination of shorter CCD-lines, has to be calibrated under flight conditions