Electromagnetic trackers are sensitive to electrically or magnetically conductive objects. If there is a metal near the electromagnetic tracker's transmitter or receiver, the transmitter signals are distorted and the resulting position/orientation measurements contain errors.

1. Calibration Issues in Studierstube
Raffaele de Amicis 1
, Michele Fiorentino 2
1
Fraunhofer-Institut für Graphische Datenverarbeitung, Darmstadt
2
Dimeg, Politecnico di Bari

2. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoIntroduction
• Electromagnetic trackers are sensitive to
electrically or magnetically conductive objects.
• If there is a metal near the electromagnetic
tracker's transmitter or receiver, the transmitter
signals are distorted and the resulting
position/orientation measurements contain errors.

3. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
Fiorentino
Topics of Discussion
• Common approach is to build a calibration table by
recording the tracked positions at known locations and
(try-)linearly interpolate between them. The assumption is
that the distortions of the magnetic field are linear within a
given sub-space.
• The disadvantage of this approach is that it requires a lot
of precise measurements to be taken in order to build a
good calibration table.

4. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
Fiorentino
Our Work
• Get distorted Data using a home made tool
• Developed a tool for converting raw datas in iv(Open
Inventor Files)
• Developed a studierstube-integrated-tracker utility for
testing the undistortion filter
• Get data with and without the filter
• Comparison and data analysis

5. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
Fiorentino
Getting Datas
• We used a wooden structure on Vr table Barco Baron
Emitter
Fasttrak
Calibration tool

6. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoSoftware
• Studierstube Undistortion filter
• Home Made tools
– converting raw datas in iv (raw2iv)
– studierstube-integrated-tracker utility for testing
.iv
Undistortion FilterTmeas raw2fsp
Tracker
TrackerBilder .raw
raw2iv Studierstube
.fsp
Test.dll

7. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoWithout Calibration ZY
• pure

8. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoWithout Calibration XZ
• pure

9. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoWithout Calibration XY
• pure

10. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoWithout Calibration ZY
• scale_and_axis_fitting_no_calib

11. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoWithout Calibration XZ
• scale_and_axis_fitting_no_calib

12. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoWithout Calibration XY
• scale_and_axis_fitting_no_calib

13. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoCalibrated:Filters
• Vt 9-7-4
• Vt_fine 12-6-8(merged)
• Others
– vienna
– arcade

14. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
Fiorentino
Calibrated:Filters Vt 9-7-4
• Vt 9-7-4

15. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
Fiorentino
Calibrated:Filters Vt_fine 12-6-
8(merged) 9-7-4
• Vt_fine 12-6-8(merged)

16. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoOthers:Vienna
• Vt_fine 12-6-8(merged)
Are this points dangerous?

17. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoCalibrated Vt (first) ZY
• vt_inverted3_4__9_4_4__radius40

18. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoCalibrated Vt (first)XZ
• vt_inverted3_4__9_4_4__radius40

19. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoCalibrated Vt (first)XY
• vt_inverted3_4__9_4_4__radius40

20. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
Fiorentino
Calibrated Vt (first) ZY-trans
• vt_inv3_4__9_4_4__radius40_translated

21. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoCalibrated Vt (first)XZ-trans
• vt_inv3_4__9_4_4__radius40_translated

22. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoCalibrated Vt (first)XY-trans
• vt_inv3_4__9_4_4__radius40_translated

23. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
FiorentinoWhat This Means
• Fixed the problem with euler-quaternion
• All raw data are in tracker coordinates
• changing the origin in studierstube(not in
tmeas) does not affect the calibration, but
just adds a translation

24. Calibration Issues in Studierstube,
Raffaele de Amicis, Michele
Fiorentino
Next Steps
• Get better datas??
• Switch to Open Tracker??