Fig.4 Program steps 
Since the control-points are not in a numerical form, they first have to 
be digitized. This is done on the drawing table of the instrument. The 
points are stored for further use, so this step is omitted in subsequent 
revision cycles. 
Depending on the requirements, up to a maximum of 8 control-points can 
be introduced. Planimetric, height and full control-points (planimetry 
and height) are acceptable. In addition, the operator can introduce up 
to a maximum of 20 points for the relative orientation if needed. 
Normally 3 iterations are sufficient for the calculation. From 
experience, the time required for the separate steps on the average: 
digitization of control-points 
measuring points on instrument 
calculation 
setting the values, control 
25 min. 
15 min. 
3-10 min. 
10 min. 
These values are certainly not definite and can probably be reduced. In 
any case we have been able to save 10-20 min. per model. 
3.4 Program tests 
Following the usual functional tests with simulated data, the program 
was tested in a first phase with regard to accuracy and stability using 
various control-point configurations. Aerial photographs were taken of 
a region typical for Switzerland (hilly to mountainous). The signalized 
points were all geodetically determined points with an average RMSE of 
+5 cm in planimetry and height. 
From this test material, a total of 30 models with a variety of control- 
point configurations were oriented and tested. The results were good for 
all of the models. After introducing the orientation settings in the 
instrument, the models were always free of parallax. The accuracy of 
the fit in planimetry was 0.05-0.15 mm and in height 0.5-1.0 m.