05 Novembre 2003 IWAA2004, CERN, Geneva, 4-7 October 2004 1

NEW DEVELOPMENTS IN CLOSE RANGE PHOTOGRAMMETRY APPLIED TO LARGE PHYSIKS DETECTORS

Antje BehrensChristian LasseurDirk Mergelkuhl

IWAA2004, CERN, Geneva, 4-7 October 2004

IWAA2004, CERN, Geneva, 4-7 October 2004 2

Content

Photogrammetric systemProject: CMS Yoke End CapMovement of principle pointExtended calibration modelConclusions

IWAA2004, CERN, Geneva, 4-7 October 2004 3

Photogrammetric System

DCS460 and DCS660 camerasAICON software packages DPA-Win and 3D StudioRetro-reflective targetsCarbon fibre scale bars

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Experiment CMS

Diameter: 14.6 mLength: 21.6 mTotal Weight: ~ 14 600 t6 Yoke End Caps

Yoke End Caps

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CMS - Yoke End Cap

6 Yoke End Caps12 photogrammetric validations in Japan after preassembly

Image acquisition: Japan, Evaluation: CERN

Diameter: 14 mThickness: 0.6 m or 0.25 m

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Photogrammetric Project

108 Reference holes equippedSpherical targets for connection24 Distance observations

12 Carbon fibre scale bars, length 1.4 m12 Tape measurements, length 5 m - 14 m

90 Images~ 3 hours

IWAA2004, CERN, Geneva, 4-7 October 2004 7

Decreasing Quality

Problem: Decreasing quality with conventional calibration model

Possible reason: Instability of interior orientation

Mechanical influences by the userHand-held shotsScaffolding, lifting device

Effects of gravityHeating of the camera

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Movement of Principle Point

Test: Evaluation of movements of the principle point

Circular objectDiameter: 2 m Depth: 0.5 m

Camera in front of wheelRotated by 15 degrees around optical axis 24 Images

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Results

Principle point not stableMovement ellipticalAmplitude

40 µm in x-direction50 µm in y-direction

Effects of gravityDeformation camera bodyMovement of CCD sensor

Position of Principle Points

2423

2221

20

1918

17

161514

1312

11

10

9

87

65

43

2

1

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.05 0.06 0.07 0.08 0.09 0.1

xh (mm)yh

(mm

)

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First Conclusions

Possible solution: calculate principle distance /principle point for each image

BUT for real objects:Lack of depthUnfavourable distribution of pointsInsufficient number of points

Weak equation system

Improved mathematical model for camera calibration required

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Extended Calibration Model

Conventional calibration model extended by Institute of Applied Photogrammetry, University of Oldenburg (Germany)

AICON 3D Systems GmbH, Braunschweig (Germany)CERN

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Image-Variant Interior Orientation

Image-variant interior orientation

Parameters introduced as observed unknownsA priori accuracy defined by user

No weak equation systemSmearing effects caused by correlations minimized

Radial-symmetric distortion A1, A2, A3

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Finite Elements Correction Grid

Finite elements correction grid

Correction ofTangential-asymmetric distortionAffinity and shearingSensor unflatness

Raster-wise correction gridCorrection as plane vector for each grid point

Curvature constraints as pseudo observationsA priori accuracy defined by user

No weak equation system

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Results - Interior Accuracy

0.50.8Sigma 0 a posteriori

1 : 110 0001 : 80 000Relative precision by interior accuracy

0.120.18RMSXYZ (mm)

ExtendedConventionalCalibration model

Enhancement of relative precision ~ 30 %

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Results – Variation of Interior Orientation

A priori accuracy interior orientation: 15 µmVariation of principle distance: 200 µmVariation of principle point: 140 µm in x-direction

90 µm in y-direction

Variation of Principle Distance

-0.16

-0.12

-0.08

-0.04

0

0.04

0.08

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89

Image Number

Varia

tion

of c

k (m

m)

Position of Principle Points

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26

xh (mm)

yh (m

m)

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Results – Finite Elements Correction Grid

Raster-width of 2.35mm 13:9A priori accuracy curvature constraints: 1 µmMaximum length of correction vector: 8 µm Tangential-asymmetric distortion

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Results - Exterior Accuracy

Residuals of Distance Observations

-3

-2

-1

0

1

2

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Distance Observation

Resi

dual

(mm

)

FiBun - Extended calibration modelDPA-Win - Conventional calibration model

t

0.17 mm0.99 mmStdev

0.85 mm4.56 mmRange

FiBunDPA-Win

1 Long distance information for scale definitionRemaining distance observation as external control

12 Carbon fibre scale bars (< 0.02 mm, 1 σ)12 Long distance information (0.3 mm, 1 σ)

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Conclusions

Project CMS Yoke End Cap, Japan

Extended calibration model Interior and exterior accuracy enhanced

Possible careless handling by untrained operator

Evaluation for different projects

Camera careful handled by photogrammetric expertsExtended calibration model

No clear conclusion possible

Further investigation how results improve significantly

IWAA2004, CERN, Geneva, 4-7 October 2004 19

End

Thank you for your attention!

New Developments in Close Range Photogrammetry applied to Large Physics Detectors

Antje BehrensChristian LasseurDirk Mergelkuhl