41 
centres: 8 full points, 4 height points. 
4.5.2 Results of the Adjustments 
The number of image, control and check points in 
both configurations was as follows: 
Table 2. Numbers of points in the adjustments 
# image 
# control points 
# check points 
points 
plan height 
plan height 
PPO 256 
53 53 
0 0 
PP2 256 
8 12 
45 41 
During the adjustments, gross errors were taken to 
be observations with a residual greater than 3a 0 . 
From the manual measurements three points were 
rejected; from the digital only two. 
All values are given in microns at the photograph 
scale. The average scale of 1:15,000 was used to 
convert the empirical RMS values (p xy ,p z ) and 
theoretical standard deviations (ct xy ,a z ) of the 
check points from object space to image space. 
Table 3. Result of the MANUAL measurement 
#APs 
<*o 
(|lm) 
M-xy 
(tun) 
Mz 
(|lm) 
(pm) 
<7 Z 
(pm) 
PPO 0 
3.3 
- 
- 
- 
- 
12 
2.7 
- 
- 
- 
- 
44 
2.5 
- 
- 
- 
- 
PP2 0 
3.0 
3.4 
5.4 
2.7 
5.6 
12 
2.5 
2.5 
4.5 
2.4 
4.9 
44 
2.2 
2.5 
5.1 
2.2 
4.5 
Table 4. Result of the DIGITAL measurement 
#APs 
<*o 
(pm) 
M-xy 
(pm) 
Mz 
(pm) 
°xy 
(pm) 
(pm) 
PPO 0 
3.6 
- 
- 
- 
- 
12 
2.9 
- 
- 
- 
- 
44 
2.7 
- 
- 
- 
- 
PP2 0 
3.2 
4.2 
6.6 
2.8 
6.0 
12 
2.6 
2.6 
4.9 
2.5 
5.0 
44 
2.3 
2.7 
4.3 
2.3 
4.7 
4.6 Discussion of the Results 
In general, the results from the digital 
measurements are slightly worse than from the 
manual. In both cases, the empirical check point 
RMS values agree quite well with the theoretical 
standard deviations from the adjustment. 
The digital version included all matched points, but 
there was found to be no correlation between the 
image space residuals and the matching results. 
Therefore, it is likely that the biases noted during 
the matching are not significant, but may contribute 
to the overall accuracy in the same way as that 
operator measurements carry a certain error. 
Adjustments without the badly matched points 
proved fruitless due to the degradation of block 
geometry. 
The major difference then from the manual 
observations lies in the calibration. The base 
accuracy level of the instrument calibration applies 
to both cases, hence the additional error could be 
attributed to the calibration of the CCD cameras. In 
particular, stability may be a crucial factor. 
A similar investigation has been done at Stuttgart 
University (Ackermann and Schneider, 1986). The 
results were similar, but cannot be compared 
directly as the aim of that investigation was a 
comparison between digital measurement of 
natural points against manual measurements of 
signalised points. 
4.7 The Potential of Semi-Automation 
This investigation raises some interesting questions 
with regard to a potential automation, or semi 
automation, of the whole procedure. This does not