Full text: Surveying and documentation of historic buildings - monuments - sites

înmeyer, Geneva 
Experiences with the Digital Photogrammetric Program Package Orpheus ... 
643 
djustment can be 
'the object can be 
, it is necessary to 
has to be covered 
non edge, and (4), 
vertices have been 
intation (B-rep) is 
: reported, and the 
ig B-rep model is 
iESTALTs can be 
by a final overall 
is projected to the 
tion closest to the 
1 inspection of the 
n model created in 
PHEUS. From the 
aside. The camera 
ie determination of 
ited in (Streilein et 
)lympus data set, a 
mb lines and from 
With respect to the 
: the facades of the 
, four GESTALTs 
e points per image 
ne is considered to 
lent (its object co- 
tional GESTALTs 
sides of the “block 
these categories of 
g different a priori 
id for modelling in 
GENT. For each of 
ariance component 
detection had to be 
part of the data set. 
lifferent facades. It 
fted with respect to 
ts remaining in the 
>01-212, and (-0.82 
in the data set. The 
it sketch in the data 
set description, but the average size of the residuals strongly indicates a systematic shift. The new co-ordinates of control points 201 - 
323 are given in table 1. 
With respect to one variant of the Olympus data set, only distances were used instead of control points to define the geodetic datum 
of the block. The distances between points 101 and 111, 111 and 121, 101 and 121, and between 301 and 321 were computed from 
the co-ordinates of these points (these are the distances which could be easily measured using a tape). They were used to define the 
scale of the block. The four vertical lines at the building edges corresponding to four GESTALTS (cf. section 3.1.1) were used to 
define the vertical axis and, thus, also to define two rotations of the block (co and (p). In order to determine the shift of the block, 
point 101 was introduced as a control point. In order to determine the third rotation (k) of the block, the y co-ordinate of point 121 
was introduced as a “control co-ordinate”. Note that the four (3+1) co-ordinates of these two points are just used to avoid 
singularities of the block. 
Point 
201 
202 
211 
212 
301 
302 
303 
311 
312 
321 
322 
323 
X 
114.93 
114.99 
116.31 
116.30 
150.08 
150.06 
150.00 
132.24 
132.26 
116.33 
116.31 
116.42 
Y 
249.06 
248.99 
237.22 
237.25 
255.11 
255.12 
255.12 
252.96 
252.99 
251.15 
251.16 
251.17 
14.68 
3.65 
14.67 
3.64 
14.72 
10.42 
3.72 
14.68 
8.30 
14.68 
10.38 
3.69 
Table 1: New co-ordinates of points 201-323 as derived from photogrammetric triangulation (Olympus data set). The r.m.s. errors of 
these co-ordinates are ±4.5 cm (X, Y) and ±3 cm (height), which is in accordance with measurements from a reflectorless theodolite. 
Self-calibration: In order to perform self-calibration, the parameters of inner orientation as given in the data set description were 
used as approximate values. The co-ordinates of the principal point were introduced as observations with an a priori r.m.s. error of 
±10 pixels. Several variants were computed using different parameterisations of the distortion polynomial. Initially, all images were 
given identical, but unknown parameters of inner orientation and distortion. There were no contradictions to this assumption in the 
Fuji data set. However, performing robust estimation in the Olympus data set, it was obvious that the tie points not being situated in 
the facades were eliminated as gross errors even though they were obviously correct. This observation and the fact that the 
distribution of residuals appeared to be systematic initiated the suspicion that some of the photos might have been taken using 
another focal length. Adjustment was repeated using individual parameters of inner orientation and distortion for all images. Of 
course, these parameters were determined rather badly (typically, the r.m.s. error of the focal length was ±50 pixels), but the results 
could be used to find hypotheses about groups of images having identical parameters. In an iterative procedure, groups of images 
were declared to have identical parameters of inner orientation and distortion if the results of self-calibration did not differ 
significantly. Two groups of images with different inner orientation parameters remained: Images 1-5 and 12-16 have been taken 
with a focal length of 1334 pixels, and images 6-11 (those showing the east facade) with a focal length of 1572 pixels. The distortion 
polygon for modifying the components (u 0 ,v 0 ) of p 0 in equation 1 depending on the co-ordinates of the principal point (u pp ,v pp ), the 
reduced image co-ordinates u and v and the polynomial coefficients (the distortion parameters) a, is given by equation 3: 
'«o' 
Ы 
ci 3 -u-\r 2 -1) + a A -u - (r 4 - l) + <7 5 -(/- 2 + 2-м 2 )+a 6 -(2-wv) + a 37 • и - (r 6 -l)+ a 3s ■?/ -j/- 8 - l) 
A 
a 2 - v + a 3 ■ v-(/- 2 -1) + «4 -v-(r 4 -l)+ a 5 -(2-/7-v) + r/ 6 - (л 2 + 2-v 2 )+r/ 37 ■ v ■(/• 6 -l)+« 38 ■ v-(/- 8 -l) 
with П = — , v = ——— , and r J = u 2 + v 2 . p 0 is the normalisation radius; it is the radius of a cucle of zero distortion. 
Po Pa 
In equation 3, a 2 corresponds to a scale of the v-axis, a 3 , a 4 , a 37 and a 38 describe a radial component of distortion, and a 5 and a 6 
describe an asymmetric distortion component. Table 2 shows the values for the distortion parameters, the principal point (u pp , v pp ) 
and the focal length/for all variants as well as the theoretical r.m.s. errors о of these parameters from self calibration. 
Camera 
Upp [pixel] 
v pp [pixel] 
/[pixel] 
a 2 
a 4 
«5 
a 6 
a 37 
a 38 
Po [pixel] 
Oc 
610.4 
-495.5 
1334.3 
- 
15.135 
-22.628 
- 
- 
14.564 
-3.398 
621.0 
Of I 
624.2 
-481.3 
1334.0 
-2.012 
-27.386 
0.196 
0.503 
-0.713 
- 
- 
621.0 
G 
±4.5 
±4.5 
±3.0 
±0.45 
±2.1 
±1.6 
±0.36 
±0.36 
- 
- 
Ofll 
608.6 
-480.7 
1572.3 
1.082 
-18.784 
4.557 
-0.497 
-0.016 
- 
- 
621.0 
G 
Fc 
±4.7 
±4.8 
±3.1 
±0.42 
±1.8 
±1.1 
±0.32 
±0.32 
- 
- 
- 
651.9 
-511.1 
1260.0 
- 
0.00075 
0.00006 
- 
- 
- 
- 
605.8 
Ff 
637.1 
-482.2 
1254.5 
0.887 
-28.504 
6.558 
0.533 
0.230 
- 
- 
605.8 
о 
±4. 6 
±4.5 
±1.8 
±1.9 
±0.95 
±0.65 
±0.38 
±0.35 
- 
- 
- 
Table 2: The parameters of inner orientation. Oc, Fc: Olympus / Fuji, calibration from the data set description. Of I, Of II: the 
parameter sets for the Olympus data set derived by self-calibration. Ff: the results of self calibration for the Fuji data set. 
Comparison of variants: The results of adjustment for the five variants are compared in table 3. Note that in each variant, variance 
component analysis has been used to achieve a realistic stochastic model. Thus, the a priori r.m.s. errors of the image co-ordinates 
indicate how well the mathematical model of adjustment fits to the data. It can be seen that with the Olympus data set, the r.m.s. error 
of an observed image co-ordinate was ±2.0 pixels and, thus, worse by a factor of two than with the variants using self calibration, 
which results in worse r.m.s. errors of the computed object points. In addition, more observations had to be eliminated in that version.
	        
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