9. CONFIGURATION
The number of circles per row is allowed to vary by 1 between odd and
even rows. The second dimension is thus the sum of circles in two consecutive
rows. All downloadable default calibration patterns have a size of
4
×
11
.
The last parameter that you have to enter when using a custom calibration
board is the circle spacing. This is the distance between the centers of two
neighboring circles. The distance must be equal in horizontal and vertical
direction for all circles.
9.9.2 Recording Calibration Frames
Once the calibration board settings have been set, you can start recording
calibration frames. A live preview of both cameras is displayed in the `camera
preview' area. Make sure that the calibration board is fully visible in both
camera images and then press the `capture single frame' button in the control
section. Repeat this process several times while moving either the camera or
the calibration board.
The calibration board must be recorded at several dierent positions and
orientations. You should also vary the distance of the board to the cameras and
make sure that you cover most of the cameras' eld of view. When recording
the calibration frames, it is important that both cameras are synchronized.
The more frames you record, the more accurate the computed calibration
will be. However, more frames also cause the computation of the calibration
parameters to take longer. SceneScan supports the recording of up to 40
calibration frames. We recommend using at least 20 calibration frames in
order to receive accurate results.
The recording of calibration frames can be simplied by activating the `auto
capture' mode. In this mode, a new calibration frame is recorded in x capture
intervals. You can enter the desired interval in the auto capture section and
then press the `start auto capture' button. If desired, an audible sound can
be played to signal the countdown and the recording of a new frame. Auto
capture mode can be stopped by pressing the `stop auto capture' button.
A small preview of each captured calibration frame is added to the `captured
frames' section. The frames are overlaid with the detected positions of the
calibration board circles. You can click any of the preview images to see the
calibration frame at its full resolution. An example for a calibration frame with
a correctly detected calibration board is shown in Figure 22. If the calibration
board was not detected correctly or if you are unhappy with the quality of a
calibration frame, then you can delete it by clicking on the
×
-symbol.
9.9.3 Performing Calibration
Once you have recorded a sucient number of calibration frames, you can
initiate the calibration process by pressing the calibrate button in the control
section. The time required for camera calibration depends on the number of
calibration frames that you have recorded. Calibration will usually take several
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