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packages designed as tools for GIS or image 
processing packages for rcmote sensing 
applications is still quite marked and the 
methods for evaluating such systems will 
differ. Heipke (1993) gives a full list of 
existing systems with references for further 
details. The main stereoscopic systems are the 
Intergraph ImageStation and the Leica DPW 
710, 750 and 770 . These offer production of 
a full range of photogrammetric products: 
digital mapping, aerial triangulation, DEMs 
and orthoimages; the image moves relative to 
a fixed reference mark. The Zeiss Phodis ST 
has been released in its fixed image moving 
cursor form and the moving image fixed cursor 
version will be available later this year. 
Less expensive stereo systems such as the 
Leica DVP and the R-Wel DMS have more 
limited functionality and accuracy. 
A number of systems are available just for the 
production of DEMs and orthoimages, often 
these are part of an image processing or GIS. 
Examples are ERDAS which is an image 
processing system closely integrated with 
ARC/INFO, PCI Airphoto ortho and Ramtek 
HI-VIEW. This type of system is often not 
fully functional and is designed for the non 
specialist user. Care should be taken to check 
the accuracy attained and the algorithms used 
as these can affect the quality of the final 
result. 
For a fully functional photogrammetric system 
to be attractive to a production organisation it 
must offer at least the same functionality and 
efficiency as an analytical plotter. The user 
will also expect additional features such as 
some elements of automation and display. At 
present the cost and availability of scanning 
equipment will also be an important factor. 
For these reasons current equipment 
concentrates on the production of digital 
elevation models and orthoimages as these are 
the areas where automation is most developed 
and where there is a growing market. Colomer 
and Colomina (1994) show that there is no 
economic advantage at the moment to convert 
to digital systems. 
Some of these systems have been developed 
primarily for use with satellite data and other 
for aerial photography. Slowly systems are 
now offering both options. 
Under the heading of hardware it must not be 
forgotten that aerial photographs must be 
scanned before they can be used in digital 
Systems. Scanners are still expensive and 
create problems of image quality and data 
handling. No doubt these problems will be 
solved in time but at the moment only 
339 
organisations with large throughputs, such as 
for orthoimage production, use high precision 
scanners. A solution for some organisations is 
the use of scanners designed for the printing 
trade such as the Sharp JX-600 which has 
limited resolution (600 dots per inch) 
instability in the scanning axes, but can 
nevertheless be used for a number of 
applications. 
Satellite data has been a catalyst to the use of 
digital data and is one of the main sources of 
input to digital systems. The principle 
cartographic product from satellite data is the 
image map. This has an aesthetic and novelty 
value as well as being a useful cartographic 
document and source of data fro map revision. 
Image maps may be compiled from satellite 
data which has been warped in two dimensions 
or corrected by geocoding which involves the 
use of a digital elevation model (DEM). 
The final specification of such products varies 
according to the producer and the intended 
market and a wide range exists. Image maps 
are now derived from commercial production 
processes. In France Spot Image produces 
the Geospot range of products through 
collaboration with IGN Espace, BRGM, 
ISTAR and Geosys. The IGN Espace concept 
is described by Galtier and Baudoin (1992). In 
Sweden, Satelitbild (a SSC company) also has 
a production flow line and at Institut 
Cartografic Catalunya (ICC), (Colomina et al 
1991) image maps are produced from aerial 
photographs and satellite data as commercial 
products. 
Line maps from satellite data are less 
frequently produced and the only well known 
example is IGN (France). For this standard 
photogrammetric mapping procedures are 
used. A number of organisations are 
developing digital mapping systems which will 
produce both line maps and image maps, for 
example at USGS (Skalet et al, 1992) and 
Canadian Centre for Mapping (CCM) (Ahac 
et al 1992). A system has been put into 
production at DMA (Warren 1992). A digital 
system for use with aerial photographs is in 
production at the ICC. 
3.2 Software 
Software for digital photogrammetric systems 
can be divided into two categories. The first is 
the orientation and display software, the 
second is the application software which 
ranges from programs for collecting digital 
elevation models through editing collected or 
imported data to a GIS.