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3 . Man-Machine Dialogue and Image Injection
User's comfort is a very important aspect of photogrammetric plotting. In prin
ciple, this is true for all topographic measuring methods; however, photogram
metric measurements deal with a considerable flow of information and user's
comfort directly influences the productivity. Normally, menus are used for the
dialogue between the computer and the analytical plotter, a technique which in
general does not call for a long training period. However, this dialogue has not
yet reached the comfort of a Macintosh, for example. On the other hand, trials
with speech command have so far not given satisfying results.
The dialogue with the computer is generally limited to a few commands during
image orientation, whereas mapping - and in particular the updating of existing
map sheets - calls for an intensive comparison between the aerial photographs
and the map. In general, the graphical map is laid on the drawing table or, for
numerical plotting, is monitored on a display unit, whereas the aerial photo
graphs are observed through the oculars of the plotter. The relation between the
two means is realized by the floating mark in the plotter and the drawing pen on
the tracing table. Consequently, a comparison between these two information
carriers can be very cumbersome, especially for the control of completeness or for
updating.
In this context, image injection represents a significant advance. In this case, a
map displayed on a monitor is injected into the optical path of the photogram
metric plotting instrument. The first image injection system was developed by
Intergraph and was presented in 1983; somewhat later, Zeiss presented its Video
system. Both systems were conceived for monocular observation, which means
that the image of the map is in register with only one aerial photograph and
shown in one ocular only. In 1986, Prime Wild GIS presented the stereo injection
system of the new analytical plotting system, System 9-AP. This stereo injection
system has been developed at the Institute of Photogrammetry of the Swiss
Federal Institute of Technology in Lausanne (EPFL); cf. fig. 1+2 and [1].
The technical requirements for an image injection system are very high and are
mentioned in this context in order to deduce the requirements for a fully digital
plotter. The image on the monitor has to be displaced in accordance with the plate
carrier in the plotting instruments; a refreshing rate of about 60 cycles/sec.
seems acceptable. The optical resolution and the precision of the geometric pre
sentation must also correspond to those of the aerial photographs. This rapidly
leads to a need for a monitor capable of handling at least 1.000 x 1.000 pixels, and
a pixel should not be larger than about 10 microns with respect to the aerial pho
tographs. For a whole model, the necessary storage space will amount to 20.000 x
30.000 pixels at least, a problem which was solved for the System-9 by special
signal processors and by the use of a virtual image memory. These few reflec
tions show the requirements already needed for the presentation of a map draw
ing. The requirements for fully digital image processing are even higher and are
difficult to meet with the means made available by the current state of the art in
electronics.
