Calibration Procedure

CAVE Line-Of-Sight Calibration Procedure

Jan. 26, 2000

Eric He

1. RUN CAVEVARS.

Make sure the tracker program is working.

Adjust “transmitter offset” in cave configure file to make (0,5,0) position is correct. The physical position of (0,5,0) in CAVE is the center of CAVE. It can be measured by tape measure. At the same time, a blue ball will appear when the head tracker is on position (0,5,0).

Try to get a rough feeling of how good the position data is. Move the wand around, compare the estimated position with the measured position by CAVEVARS, we can get the rough feeling.

Make sure the magnetic field does not “fold back” on itself. Our calibration method can only correct “non-fold-back” distortion. Move the wand along x, y, and z axis, if the data measured by CAVEVARS is changing monotonously, the CAVE can be calibrated.

2. Position physical targets.

Put three physical targets of 5 feet height on positions (-2, 5,-3), (0, 5, -3), and (2, 5, -3) feet.

3. RUN CAVE_MEASURE (~eric/cave/calibration/pos/src/CAVE_MEASURE)

You will find three virtual dots. If the magnetic field has not any distortion, the three white dots will match the three physical targets perfectly. But in normal situations, the position data contains more or less error. Therefore, the white dots will not match the physical targets exactly. You can push down the left button of the wand and move wand to move the white dots until they are matched. And enter the correction by pushing the right button of the wand after you are sure that the dots are matched. (NOTE: Do not push the middle button, which will exit the calibration program.)

Do the same correction procedure around the CAVE. The times of correction depends on the initial quality of position data. Normally I do 20-30 times. If the initial situation is really bad, the times could be above 50.

Finally, push the middle button to save all correction data and exit the program.

4. The generated lookup table file is corr.table. Rename it to a suitable name and copy it to /usr/local/CAVE/etc/cal/.

5. Modify the configure items in CAVE configure file. Make sure the item “Calibration” is “y” and “CalibrationFile” is the right file.

NOTES:

The initial lookup table file is c4tab. This file specifies the cube we will calibrate in tracker coordinate system. Therefore, the file needs to be modified if the transmitter position is changed.

The detail of line of sight method and the options of “measure” program please refer to Marek’s article.