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Systems for data processing, anaylsis and representation

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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
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
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
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
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.