)TM 
'he 
Ar 
T 
ing 
ill 
Ly, 
ap— 
ITC 
nts 
on, 
ISPRS-Symposium Commission II 
Baltimore, May 26-30, 1986 
Rechner-unterstützte Punktmessung am Analytischen Plotter 
Dr.-Ing. Karl Heiko Ellenbeck 
Institut für Photogrammetrie 
der Universitat Bonn 
Nussallee 15 
D-5300 Bonn 1, Federal Republic of Germany 
Abstract 
Computer-assisted Point Measurement with an Analytical Plotter 
Point measurement (e.g. Aerotriangulation) with an analytical 
plotter (A.P.) consists of seeking and identifying, precise 
measuring and coding with a point number. To seek and to 
identify a point and to look for errors is time consuming and 
delays the progress of work. Most errors of tie points in 
aerotriangulation originate from wrong point coding. 
The aim of the computer assisted point measurement is to use 
the automatic carriage positioning of the A.P. and to introduce 
an automatic identification and coding. Carriage positioning is 
possible, if the approximate photo coordinates are digitized on 
a graphics tablet from contact prints during the preparation of 
aerotriangulation. For regularly shaped blocks of photos an 
interactive program can control the distribution and coding of 
tie points by 2D-transformations. In doing so the input of 
point numbers is necessary, if at all, only the first time the 
point occurs. 
After such preparation with a low-cost digitizer system all 
points can be identified by photo coordinates and controlled 
point numbers. The photo connections are checked. Just as well 
gross errors of control point coordinates can be detected. The 
point measurement with the more expensive A.P. is reduced to 
precise measuring of automatically positioned and coded points. 
The experience of 3 years and more than 10.000 models in 
aerotriangulation results in a reduction of more than 50% of 
working time at the A.P. and about 30% of runs of block 
adjustment. 
43