International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004
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3.3 Calibration contents in multi-camera system
Though the principle and technique of CCD cameras is quite
different from that of common analog cameras, the two
categories are similar in calibration specifications and method.
However, the calibration contents vary from different purposes.
As for our multi-camera system, the following items are
calibrated first : The inner elements of each camera: principal
point( x, , yg )and principal distance(f);The optical distortion
parameters : radial distortion factors( Æ, , &, ,...) and eccentric
distortion factors( p, , p, ).
After the inner elements and distortion parameters of each
small-sized CCD camera has been obtained using the solution
of space resection with multiple images, the cameras are
mounted onto the platform specially designed for
multi-camera combination system and they are electronically
controlled to take the images of the same calibration field
simultaneously. With these data, real exterior elements: linear
elements( .X , , Y; , Z, ) and angle elements ( 9 , & , K ) of the
multi-camera system, relative exterior elements of each
camera to the principal optical axis of equivalent image
(0.,0,,0., d$, dS, dS. ) are to be determined.
3.4 Multi-camera system correction
The following corrections are indispensable for practical system.
The corrections are based on system calibration results.
1) Exterior elements correction
The correction component of exterior elements
(dS, d$, dS. , dO y ,dOy, dO; ) is the difference between
system design value and its corresponding calibrated value.
2) Image coordinates correction
Denote corrected image coordinates as (x,y), observed image
coordinates as ( x;,,, V;, ).radial distortion factor as k, . (Since
our multi-camera system use small-sized non-metric CCD
cameras, we can take the radial distortion factor Æ, into
consideration only.) Suppose 7r is the radius from image point
to principal point. Then correction model for image correction
is:
PEE C ef = =
E =2m = Xo Tl 7 Xo)!
Yt , — , — , À
X -m—y m Yo t Ki Cy im Yo )r
Where, r? zx Ex + (Vim — y)”
un
3) Equivalent image correction
The equivalent image coordinates (x , y) is calculated on the
basis of (x'y'). Further, (x , y) needs to be corrected by
correction component of exterior elements. The correction
equation is:
;
X N Xy
dx z ds y ys +f + pi * Wx * yd;
ex diet Ads; rf do, + 77.46, t xd6;
4. EXPERIMENTS
The following experiments are carried out to test and verify
the above mentions.
Four FUJIFILM FinePix 4700zoom areal CCD cameras are
used in the experiments. FinePix type is characterized by small
size, handy use, high light sensitivity, large storge
etc..especially, the capabillity of locking principal distance.
3 and 4 FinePix 4700zoom cameras are mounted on
experimental multi-camera platform to construct the 3-camera
combiantion system (Fig. 12) and 4-camera combination
system (Fig. 13).
Fig. 12: 3-camera system Fig. 13: 4-camera system
Table 1 gives the result for each single camera
calibration. The cailbration is done through outdoor
Interna
calib
resec
Notes
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Fig.1:
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