Equipment
In 1991 at the ISPRS symposium on Digital Photogram-
metric Systems [5] a comprehensive review of current
digital systems was given. Table 1 gives an updated
version of the systems on offer.
Most current systems are based on standard work
stations. The present generation of workstations with
graphic accelerators and stereo viewing as standard pro
vide most of the features necessary for digital photogram-
metry. Using off the shelf hardware adds to the possibility
of transportable software which is highly desirable. Some
manufacturers prefer to use dedicated hardware and this
approach has led Intergraph to be one of the leaders in
the market. Other users have developed systems for their
own particular environment as close range systems (for
example at ETH, Zürich, [9]) and at USGS [20], Canadian
Centre for Mapping [1] and Defense Mapping Agency
Table 1. A classification of digital photogrammetric workstations for
production work.
NGT GEODESIA 93 - 8
(DMA) [22], where large automatic mapping systems are
under development.
An important development is the production and use of
image maps. Many organisations have produced experi
mental image map sheets and now national mapping
agencies and private organisations have established a
production system for such maps. IGN in France [8] has
notable examples and the production systems mentioned
in the previous paragraph at USGS and CCRS are
planned to include such a facility. Orthophoto production
is not always necessary if the terrain is flat, but in a full
production system the capability for relief correction must
exist. A user interface is also required in order to monitor
the stages of production and particularly the mosaicing.
If DEM production is included in the system then this
must also be validated.
There are still problems to be overcome. Operators name
the quality of the image as a problem although this is
difficult to quantify. The DSCC, developed for the DMA,
reputedly has a very high standard display which uses
epipolar images and high resolution. This leads to high
costs but the question of whether such features are
necessary for general acceptance of the systems has not
been answered. The DCSS uses stereoscopic eyepieces
whereas the trend with the current generation of systems
is to use electronic shuttering. However, experience does
suggest that the least expensive, anaglyph display has
many shortcomings.
A report of the activities of ISPRS inter-commission
working group ll/lll, Design and algorithmic aspects of
digital photogrammetric systems" [4] reported a number
of areas where more work is needed:
faster display for stereo viewing including continuous
roaming, zooming and image rotation;
improved possibilities for interactive measurement of
image co-ordinates with sub-pixel accuracy;
simultaneous use of more than two images;
use of data from different sensors;
continued development of algorithms for robust image
matching and feature extraction;
improved integration with GIS;
improved human interface.
Although ISPRS working groups are aware of the tech
nical shortcomings, there is still scepticism amongst map
producers who do not feel that there are yet significant
advantages in moving to digital systems.
Software
As noted above software is the key to a successful devel
opment. Software for digital photogrammetry is of three
types
display and interface software;
software for the standard photogrammetric opera
tions;
software for automation.
Display and interface software are clearly important and
the quality will depend to a large extent on cost, both of
the hardware platform and on the software, refer again to
the DSCC. X-Windows is becoming an industry standard
and as such is becoming increasingly important.
The basic algorithms for photogrammetry may not appear
to need redesigning for digital workstations but maybe
369
SYSTEM
COMMENTS:
Performance and functionality of analytical plotters with
image processing
and computer assisted feature ex-
traction.
DSCC
Powerful purpose built systems; devel
oped for defence agency. Uses hard
wired components.
HAI-750 HAI-500
Two full photogrammetric systems on
Sun or PC platform.
Leica DSP1
Analytical plotter concept based on
Gems image processing system.
Matra T10
Analytical plotter concept Intergraph
ImageStation. Photogrammetric data
capture as part of digital mapping
system.
Systems designed for specific applications with high per
formance but limited functionality.
Autometrics
Software for DEM extraction and editing
Pegasus
on Silicon Graphics Workstation. De
signed as open system.
HAI-DCCS
Digitizing of photographs for tie point
selection and matching.
USGS
Workstations incorporated into digital
mapping system for mono-plotting from
ortho-Images.
CCM/MDA
Workstations incorporated into digital
database revision system for mono and
stereo feature extraction.
PS PRPSM
Interface for orthophoto production.
Eurosense Eudicort
Interface for orthophoto production.
ICC
Institut Cartographic Catalunya Inter
face for orthophoto production.
Signum
Interface for orthophoto production.
ISTAR
Interface for automatic DEM generation.
UCL Geodem
Interface for automatic DEM generation.
Map Vision
Automatic extraction of target co-ordi
nates.
Rolleimetric
Automatic extraction of target co-ordi
nates. Limited performance and functio
nality but low cost.
R-Wel DMS
PC based system for DEM and feature
extraction from images as input to and
integration with a GIS.
Leica DVP
PC based system for digital mapping
from aerial photographs.
