(WIMP) environment. The problems of stereo display and scrolling have already been discussed.
Photogrammetric software can be easily transported to digital systems since the operations tire
basically the same. New camera models may be needed for SPOT or SAR, but again these have
been developed in other environments.
It is the area of real time support that the real challenge lies. Automatic identification of ground
control points using map data has proved to be a significant problem, even with image data from
other sources matching is not always possible although the increasing use of DEMs and simulation
techniques offers a way forward. Techniques of image enhancement are well developed but speed
of implementation is important if the system is used in real time with CCD cameras on line. Feature
extraction is a far more difficult problem although steps are being taken in this direction (Perlant
and McKeown 1990, Forstner 1989). Kem have implemented line following with the x parallax
being removed on the DSP1, the required speed has been achieved with the use of transputers.
Much effort in recent years has been put into speeding up image matching so that SPOT images for
example, can be matched to produce a DEM in a few hours. This now seems to have been
achieved using transputers as shown by Collins and his co-workers at the Fast Processing
Workshop, but this brings with it the need to manipulate and check the resulting DEM. DEM
packages are well developed and visualisations in wire frame perspective can be produced quickly
but more realistic visualisations in whickh the scene is rendered by shading techniques or merged
with images required more speed. Animation puts even greater demands on the hardware and the
ingenuity of the programmer.
Integration with GIS and LIS
Photogrtammetric methods of data capture in stand alone systems do not make sense any more.
The photogrammetric data must be used with other data in a digital mapping sytem, LIS or GIS to
be used to the full. The impact of this on the DPW is that it must be compatible with other systems
and the data must be in a form which can be used by such systems. Data from GIS can in turn
contribute to photogrammetric data capture as work by Van Cleyenbreugel et al (1990), for
example, on delineating road structures shows.
Conclusion
This paper has set out to show the progress made in the development of digital photogrammetric
workstations. There is evidence of two trends. First to produce a system which is has restricted
functionality and power but is less expensive although it is evident that the more expensive
workstation such as Sun can be use in thisa way with much the same functionality as the universal
instruments. Second to look for alternative hardware to speed up the photogrammetric problems.
This latter approach required co-operation with other disciples and flexible thinking. The main area
for future deveopments in is software to spped up off line processes such as GCP identification and
feature extraction.
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