For considerably more detail on the current status of map 
revision than can be included here, readers are referred 
to that article, which was designed to set the scene for 
this Congress. However, since that paper is also in 
large part a review of Working Group progress during 
this session, many of the points made there should also 
be emphasised here. 
In the digital photogrammetric revolution, as in all 
revolutions, forces of reaction are also at work, based in 
this case on sound economic and practical grounds. In 
the real world of routine production, all technical 
processes stand or fall by their cost effectiveness. This 
is especially the case with entirely new developments 
such as softcopy photogrammetry because of the high 
initial investment involved, not only in research and 
development and in capital equipment (including the 
scanner as well as workstations), but also in staff training 
and (most importantly for database revision) in 
integration with existing systems. Unless on taking all of 
those factors into account digital photogrammetry can do 
a better, cheaper or quicker job than existing methods, 
the latter must be retained. To justify the change, at 
least one, but preferably two or three of those 
comparisons must be proved to be favourable. 
Moreover, the needs and wishes of map and data users 
must be both recognised and embedded into the 
implementation of any technical change. It is 
encouraging that several of the contributions to this 
congress do emphasise these points, when discussing 
progress towards their goal of automation. If these 
matters are fully appreciated we can move on to consider 
current directions in research, and their antecedents. 
It is developments in computer science over the past 
forty years which have provided the driving force for 
development in surveying and mapping, including (or 
indeed especially) in photogrammetry. We have moved 
from totally analogue optical and mechanical processes, 
through the first steps in analytical aerial triangulation in 
the 1950s and 1960s, to the late-80s situation in which 
the misleadingly named "analytical plotter" had become a 
photogrammetric workstation at which a human operator, 
assisted by one or more computers, could capture or edit 
three-dimensional geometric, topological and semantic 
data about the world from collections of high quality two- 
dimensional graphic images and. record it in digital 
databases (Bonjour & Newby, 1990). 
Meanwhile our colleagues developing the newly emerging 
discipline of remote sensing were obliged generally to 
use digital images transmitted from satellites. 
Developments in computer science parallel to those 
exploited by surveyors and mappers allowed them to 
learn to handle such images. Image processing and 
computer vision developed independently of 
photogrammetry for the simple reason that 
photogrammetrists retained the major advantage of 
working with graphic images of very high geometric and 
radiometric quality; only very recently have 
developments in computer graphics made digital images 
worthy of the attention of photogrammetrists. Now there 
is a most welcome convergence between 
photogrammetry and remote sensing, image processing 
and computer vision : for it is clear that photogrammetry 
can benefit from existing expertise in digital image 
600 
processing, while contributing traditional strengths in the 
rigorous understanding and manipulation of the geometry 
of image formation. 
Benefiting from this convergence, numerous system 
vendors now offer softcopy systems capable of handling 
many photogrammetric tasks. However the papers at 
this Congress demonstrate that database update is a 
considerably more complex task than database creation. 
Vendors, even if they have grasped this distinction, are 
not yet providing ready-made solutions to the update 
problem, but it is those who are willing to work closely 
with users to integrate revision systems into existing 
technical and management structures who will be most 
successful in this fundamental future activity. 
4. SCANNERS, SENSORS AND WORKSTATIONS 
In the present structure of ISPRS it is clear that 
developments in image capture and manipulation belong 
to other Working Groups in other commissions. 
However, such developments will naturally influence the 
directions taken by their eventual users. Thus a review 
of aspects of digital photogrammetry relevant to map and 
database revision is necessary here. For more detail, 
again refer to Newby (1996). 
It is not feasible to enter digital photogrammetry half- 
heartedly. To justify the investment in a scanner to 
convert photographic hard copy images into softcopy it is 
necessary to plan to make use of its full capacity. | 
would expect one scanner to be able to supply four to six 
digital photogrammetric workstations (DPWS) although 
there is not yet much practical experience to quote in this 
connection. It remains an open question whether it is 
necessary to spend the large sums required for a top 
quality scanner designed expressly for photogrammetry, 
or whether much lower cost systems can give acceptable 
results. Certainly it is now recognised that not all 
scanners are the same, that even very expensive 
scanners may not provide perfect results, and that the 
complete digital photogrammetric flowline will depend on 
this single crucial component. The importance of this 
issue led to the formation of a joint OEEPE-ISPRS 
working group on the analysis of photo-scanners. 
This group has examined not only the technical 
requirements of geometry, resolution, image noise, 
dynamic range and so on, but also comfort and 
convenience aspects such as the level of automation of 
the process and the use of original roll film negatives, as 
well as engineering points involving the satisfactory 
solution of classical problems of aerial imagery such as 
optical distortion, image flatness, vibration and the 
avoidance of artefacts. Above all, the results of 
scanning must aim to be as good and cheap as a 
diapositive! (Kôlbl et al, 1994). 
This makes it quite hard for digital photogrammetry to 
compete. Photogrammetric operators are now 
accustomed to recent improvements in photography such 
as forward motion compensation (FMC). FMC not only 
allows photography to be flown under conditions which 
would in the past have been considered marginal (a 
major factor for time-dependent map revision) but it also 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
  
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