Cl PA 2003 XIX th International Symposium. 30 September - 04 October, 2003, Antalya, Turkey 
significant. The a priori standard deviation was set to 1 pixel (= 
0.006445 mm) for all experiments. 
Focal length and principle point 
Lines of three vanishing points are required for the focal length 
and principle point estimation. The lines were extracted and 
grouped automatically by vanishing point detection, and also 
measured manually (Figure 3). The estimated parameters using 
the results of each image separately were not consistent (Image 
3 and 6 as an example in Table 1). Especially the difference in 
the estimated focal length was considerable. 
Image 3 
Image 6 
Image 3 
Manual 
Image 6 
Manual 
Variance fac. 
1.027 
0.903 
1.152 
0.132 
d.o.f. 
487 
454 
7 
7 
Max. residual 
0.018 / 
0.018 / 
0.010 / 
0.003 / 
(mm / pixel) 
2.8 
2.8 
1.6 
0.4 
Focal length 
8.668 
9.663 
8.514 
10.092 
in mm (a) 
(0.052) 
(0.079) 
(0.046) 
(0.058) 
Princip put. y 
-0.200 
-0.053 
-0.085 
0.376 
in mm (a) 
(0.057) 
(0.067) 
(0.066) 
(0.076) 
Table 1 : Results of camera parameters estimation using 
automatically and manually extracted and labeled lines. 
The location of the principle point could not be estimated in x- 
direction due to the near two-point perspective of the imagery. 
The precision of the parameters estimated from manual 
measurements is better, although the number of lines used is 
only a fraction of the number of automatically extracted lines. 
The reason is found in the length of the manually extracted 
lines. Therefore, hereafter only the manually extracted lines are 
used for the camera calibration. This choice is also to be 
preferred because it limits the assumptions of parallelism and 
perpendicularity to the measured edges of the building. 
The source of the inconsistency was traced by estimating the 
parameters using the manual measurements of combinations of 
two images. The results are shown in Table 2. Only the fit of the 
combination in which image 3 is missing is of good quality; the 
overall test is accepted (critical value 1.93). 
Imag 3-6 
Imag 3-11 
Imag 6-11 
Variance factor 
31.01 
31.63 
1.435 
d.o.f. 
16 
16 
16 
Max. residual (mm / 
0.058 / 
0.052 / 
0.012 / 
pixel) 
8.8 
8.1 
1.8 
Focal length in mm 
9.124 
9.234 
10.056 
(o) 
(0.035) 
(0.032) 
(0.037) 
Principle point y in 
0.158 
0.028 
0.267 
mm (o) 
(0.048) 
(0.046) 
(0.050) 
Table 2: Camera parameter estimation using the manual 
measurement of combinations of images 
Image 10 was now added in the estimation in order to verify the 
results. In Table 3 adjustment results using the manual 
measurements of three images are presented. As the critical 
value is 1.8 (5% significance level) both adjustments are 
accepted. Due to the 90 degree rotation around the optical axis 
of image 10 the principle point x co-ordinate can also be 
estimated. Note that the manual line measurements are not 
suitable for estimation of lens distortion. The results in the last 
column of Table 3 are the final estimates of the camera 
parameters used for image orientation described in the next 
section. 
V 
Figure 3: Manual line measurements for camera calibration 
(images 3 (top) and 6) 
Image 6, 10, 11 
Image 6, 10, 11 
Final 
Variance factor 
1.553 
1.211 
d.o.f. 
26 
25 
Max. residual (mm 
/ pixel) 
0.0131/2.0 
0.0100/1.6 
Focal length 
10.103 
10.116 
in mm (a) 
(0.029) 
(0.030) 
Principle point x 
- 
-0.146 
in mm (o) 
(0.041) 
Principle point y 
0.222 
0.220 
in mm (a) 
(0.047) 
(0.046) 
Table 3: Camera parameter estimation using the final 
combination of three images 
The CIPA data set was also analysed by others (Streilein et al., 
2000), (Rottensteiner et al., 2001). In the paper by Rottensteiner 
the images taken with the Olympus camera are split in two 
groups, one with a focal length of 8.598 mm and the other with 
a focal length of 10.132 mm (balanced lens distortion). 
Obviously, the setting of the zoom lens is different for the two 
sets of images. The camera parameter values from (Rottensteiner 
et al., 2001) derived with bundle adjustment software Orpheus, 
are used as a reference. Comparison with camera parameters 
provided in this set showed a good match. The lens distortion 
parameter is not compared because the number and definition of 
distortion parameters differs in the set determined with Orpheus. 
The difference in the focal length is 3.0 times its standard