supported plotter, the so-called *Hybrid Plotter" (3), (4). A computer 
generates corrections for y-parallaxes and for model deformations. Another 
interesting development was initiated in about 1970 by the University of 
New Brunswick, Canada (5). A conventional plotter was interfaced with a 
table-top calculator serially. Later another plotter was interfaced with a mini- 
computer, and feedback loops with the plotter were considered (6). The 
concept of real hybrid systems was first formulated in 1968 at the ITC (7). 
However, the first hybrid plotter, i.e. the HO—1 Plotter of Messerschmitt- 
Bólkov-Blohm, was introduced by O. Hofmann at the ISP Congress in Ottawa, 
1972 (8). In this evolution the involvement of digital components has 
gradually grown from the control of digital data generation and recording, 
to rather complex data processing and adaptive controls. The recent efforts 
have been directed mostly towards interfacing photogrammetric instruments 
with table-top or mini-computers serially. Some limited effort has also been 
directed towards interfacing the components with feedback loops, and thus 
to create conditions for adaptive controls. The present trend is to replace the 
conventional precision instruments partly by the fully digital type 
systems (i.e. analytical plotters) and partly by the computer supported topo- 
graphic plotters. 
In the following chapters some basic considerations on the computer 
supported instruments will first be presented. This will be followed by a 
survey and outline of the equipment components and of the corresponding 
software. The central topic, however, will be the different system configu- 
rations. A short outline of the existing systems will be included. Finally some 
development trends will be reviewed. 
II General Considerations 
The technical objectives for implementation of a computer supported 
instrument are: increased speed, precision, flexibility, versatility, improved 
operational characteristics, removal of gross errors and replacement of 
erroneous data, uniform quality of outputs and conditioning of output data 
for further use. 
The basic prerequisite for achievement of these objectives are well 
designed interactions between the three main components of a system (fig. 1). 
The interactions between analogue and digital components should possibly