Table 3: Testblock Appenweier, precision and accuracy results after 
bundle block adjustment with 12 additional parameters 
  
tie-points from check points 
Version | measurement point transfer 99 Wy uy Hy y u 
[um]| [um] — [um] (um ] — [ym] 
  
a operator no 3.3 7.6 5.4 6.6 14.5 
C100 (sign. points) 
b dig.correlation yes 4.0 73 773 73 9.8 
C 100 
  
  
  
  
  
  
  
Assessing the results we look first at the g, values of 3.3 ym and 4.0 
um of version a) and b), respectively. The difference is almost entire- 
ly caused by the digital point transfer. It can be concluded, there- 
fore, that the transfer of natural tie points by digital image correla- 
tion contributes to the total error budget of the image coordinates 
with a r.m.s. value of 2.3 um. (If the setting errors of the signalized 
points still included in version b) are considered the r.m.s. value in- 
creases to 2.4 ym.) 
The absolute accuracy of the adjusted blocks a) and b) (signalized tie 
points without point transfer against natural tie points with digital 
point transfer), as assessed from the 23 planimetric check points, is 
represented by the r.m.s. values of Urine 6.6 um and Ry yf 7.3 um, 
respectively (or 6.3 pm and 7.0 ym, cóifdidering the inacéuracy of the 
check points). Thus, the additional contribution of digital point 
transfer to the absolute planimetric accuracy of the block amounts to 
3.1 um. The comparison with regard to the vertical accuracy (14.5 um 
against 9.8 um) is contradictory, as the block with digital point 
transfer has, in this test, considerably better vertical accuracy than 
the block with signalized transfer points. The apparent incongruency 
may be caused by the small number of only 10 vertical check points. It 
cannot be considered significant. Remark: The results of version a) 
(signalized points, operator measurements) differ from previously pub- 
lished results of the total test block Appenweier, which were more pre- 
cise /6/. The differences may have several reasons (13 years old photo- 
graphy, different geometry, different control points, tie points and 
measuring instruments). They are of no particular concern here, as this 
test is primarily looking for the performance of digital point transfer 
against a comparable set of manual measurements of signalized tie 
points. 
4. CONCLUSION 
The experimental investigation attempted to demonstrate and confirm the 
high accuracy capability of digital transfer of natural tie paints by 
digital image correlation. The experiments were carried out with 2 
small blocks of black and white, wide-angle photographs (Schnürpflin- 
gen, 26 photographs, 1:4 000 and Appenweier, 28 photographs, 1:7 800). 
In both cases the results of manual measurement of signalized tie 
points were compared with digital transfer of natural tie points. The 
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