9. CONFIGURATION
P
1
and
P
2
: projection matrices in the new (rectied) coordinate systems.
Q
: the disparity-to-depth mapping matrix. See Section 8.2 for its use.
T
: translation vector between the coordinate systems of both cameras.
R
: rotation matrix between the coordinate systems of the left and right cam-
era.
The camera matrices
M
1
and
M
2
are structured as follows:
M
i
=
f
x
0
c
x
0
f
y
c
y
0
0
1
,
(1)
where
f
x
and
f
y
are the lenses' focal lengths in horizontal and vertical
direction (measured in pixels), and
c
x
and
c
y
are the image coordinates of the
projection center.
The distortion coecient vectors
D
1
and
D
2
have the following structure:
D
i
=
k
1
k
2
p
1
p
2
k
3
,
(2)
where
k
1
,
k
2
and
k
3
are radial distortion coecients, and
p
1
and
p
2
are
tangential distortion coecients.
You can download all calibration information as a machine-readable YAML
le, by clicking the download link at the bottom of the `calibration data' sec-
tion. This allows you to easily import the calibration data into your own
applications. Furthermore, you can save the calibration data to your PC and
reload it at a later time, by using the `upload calibration data' section. This
allows you to switch between dierent cameras or optics without repeating the
calibration process.
You can also perform a reset of the calibration data by pressing the `reset
calibration' button. In this case, image rectication is disabled and the unmod-
ied image data is passed on to the stereo matching algorithm. Use this option
when selecting the already rectied virtual example camera, as explained in
Section 7.6.
9.11 Auto Re-calibration
On the `auto re-calibration' page, which is shown in Figure 25, you can enable
an automated estimation of the camera calibration parameters. In this case,
the cameras remain calibrated even if their alignment is subject to variations.
For this process to work, it is necessary that the cameras have been calibrated
once before with the manual calibration procedure (see Section 9.9).
Calibration parameters are usually divided into intrinsic parameters (focal
length, projection center and distortion coecients) and extrinsic parameters
(transformation between the poses of both cameras). Auto re-calibration only
36