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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004 
4.1 The Model Formation In table 3 the comparison of the sd. of the point co-ordinates 
by 2*1 adjustment with 3Dom adjustment. The low accuracy 
of the co-ordinates adjusted with traditional computation, can 
be explained with the fact that the theodolite stations are 
poorly linked together by reciprocal observations, not using 
the suitable equipment. : 
The final adjustment with 3Dom has been preceded by the 
computation of the approximate co-ordinates with the model 
formation. The possible models were the combination of 17 
coupled three by three (17/3)=680 and the combination of 17 
coupled two by two (17/2)=136 , in total 816 possible 
topographic models could be formed; in reality only 27 of 
have been created by tri-section (three vertices), the 
remaining 29 by bi-section (two vertices). All of them have 
been oriented in the same reference system keeping fixed two 
vertices of the traverse. In this way the approximate co- 
ordinates of the points have been computed. In the following 
table the comparison between the co-ordinates by blind 
traverse and those got from the final 3Dom adjustment. 
Table 1 -Model Co-ordinates /Vs 3Dom co-ordinates (m) 
1) sx= .062 sve i0 - sz =.0.034 
2) sx2— .008 sy2= .140 sz2= .0.058 
3) sxa= .074 sya= .129 sza= .0.0.92 
1) sx = sample mean 
2) sx2=RMS value 
3) sxa=mean absolute values 
  
In figure 6 the differences are shown, amplified 200 times. It 
is evident a systematic effect. Figure 7 - The complete network 
Table 3 — Comparison RMS value for sd of all points 
  
  
  
RMS value (mm) | ox 9, 0; 
2+1 adjustment 34 24 14 
3Dom 2 2 1 
  
  
  
  
  
  
  
Figure 6. — The differences (amplified 200 times) between 
the model co-ordinates and 3Dom co-ordinates- 
4.2 The final Adjustments: 2+1 vs 3Dom 
Two different types of adjustment have been performed, one 
with the traditional procedure where the planimetric 
computation takes place before the altimetric one iteratively. 
The used software was RETE (Fangi, 1996). The second 
adjustment by 3Dom software after removing all the 
reciprocal observations between the traverse vertices. 3D 
adjustment has the disadvantage to require more computer 
memory compared with 2+1 adjustment. 
Due to the limited capacity of the computer Ram (512 
Mbytes), all the points have been divided in three groups and 
the computation performed separately, taking some common 
points like the station points and those points with the 
maximum frequency. The features of the three adjustment 
blocks are shown in table 2 
  
Figure 8. The central part of the control network of the 
Guggenheim museum in Bilbao with the ellipsoids of errors 
The accuracy improves especially for narrow angle resection 
  
  
  
  
  
in space. In table 3 the sd. of the adjusted co-ordinates of far | id 
Table 2 — The three groups of adjustment station point are shown. i À 
- | N points | Equations | Unknown | Redundancy Sd of the co-ordinates of the Far Stations — Comparison | 
Group 1 128 812 404 408 traditional 2+1 adjustment /vs. 3Dom adjustment (m) n 
Group 2 215 875 648 227 | 
Group 3 278 1234 838 396