the payload is equipped with a second GPS receiver
(TRIMBLE 4000SSE) with a special airborne antenna
positioned exactly over the master camera. It serves the
purpose of recording the raw phase measurements
together with the exact mid-exposure pulses of the cameras
for determination of the exact projection centres through
post-processing.
The performance of the aerial photo service has practically
been doubled through improved navigation in comparison
with the previous aircraft. Moreover the working conditions
for the pilots and the operator have improved significantly
due to the pressurized cabin. Flight planning and navigation
today are based exclusively on co-ordinates. The mean
position accuracy of a photograph with respect to the flight
plan is approximately 50 metres (even when degraded by
selective availability of GPS satellites).
1.2.2 The topographical information system
We define the topographical information system (TIS) as
that part of a GIS which contains the topographical data set
of Switzerland. The information density corresponds
approximately to that of map scales ranging from 1:10'000
to 1: 25'000.
Differential GPS navigation is developing rapidly into a tool
which requires digital maps of equivalent accuracy.
Independent of the map scale the GPS position of
manmade objects today can be determined with an
accuracy of around + 1 meter. We therefore are ultimately
aiming to provide digital maps of the same accuracy.
Today mainly the military sector is demanding digital data
with great urgency. Therefore a two phase solution was
chosen as a compromise. In a first step the contents of the
map 1: 25'000 are being digitised with an object position
accuracy ranging from 2.5 to 7.5 metres, corresponding to
the achievable accuracy at this map scale (map derived
landscape model). According to our planning this data
collection should be finished by the year 2000.
In a second phase the position accuracy will be improved to
approximately 1 metre by adjusting to precisely defined
objects (roads and buildings) and at the same time 3-
dimensional data acquisition of certain objects will be
realised (landscape model derived from reality). Most
probably this will be implemented within the scope of data
revision. In this respect we are confident that further
developments in image analysis will provide an appropriate
set of tools (e.g. feature extraction) which will satisfy our
practical needs.
Vector data set VECTOR25
To accomplish the first phase we have built up a task force
of 7 specialists in the last year, who are digitising the
contents of the 1:25'000 national maps to satisfy the
specific military needs. The resulting data set is
denominated VECTOR25. This is being realised on the
background of our pixel maps (scanned national maps) with
the line following software from LASERSCAN. For
automatic extraction of buildings, characters and symbols
we are planning to use the KAMU/AUTOVEC pattern
recognition and vectorising software developed at the ETH
Zurich.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996
Height model DHM25
The height model DHM25 which we have been working on
since quite some time will be finished this year. In the
framework of an R&D project the ETH Zurich has made
important improvements to the software program on which
the basic model of the DHM25 is based. The DHM25
consisting of digitised contour lines, bathymetric contours of
the lakes and single height points (and in the future also the
main alpine break-lines) has been converted into a height
matrix with a 25 meter grid. Additional improvement will be
brought to the height model through the photogrammetric
processing of the main break-lines of the Alps.
The basic height model and the matrix model are now being
managed with the program system SCOP.TDM which is
based on the topograpical database TOPDB from the
University of Vienna.
1.2.3 Transition from analogue to analytical photogram-
metry
Contrary to all scientific and technical papers appearing
everywhere which report about the blessings of digital
photogrammetry our practical day to day restitution still
seems to live in an old-fashioned world. The Federal Office
of Topography has 6 analytical plotters of the type WILD
BC3 working day in day out. The last A8 was sold in 1994.
Map revision requires a high degree of qualified
interpretation of what can be seen in the aerial photograph.
For this the optical viewing system of an analytical
instrument is far superior to the viewing system of digital
workstations. A modern aerial camera system combined
with the right film emulsion today delivers a resolution of
approximately 100 Lp/mm. If the same resolution was to be
achieved digitally a scanning resolution of 5 microns would
have to be imposed which would lead to enormous image
files of over 2 Gigabyte per black and white photograph.
Even in the most advanced workstations this amount of
data cannot be handled economically.
On the other hand digital systems can be put to work
economically for aerotriangulation, for the production of
geo-coded image mosaics (digital orthophotos) and for the
automatic determination of height models (DTM) through
image correlation. The Federal Office of Topography is
currently evaluating such a system consisting of an image
scanner, a high-performance computer with adequate
storage capacity and a stereo workstation. Acquisition of
the system will take place this year. High priority is being
given to a customer oriented archiving concept for digital
image data. Within the framework of a research program
together with the Centre for High-Performance Computing
at the ETH Zurich new solutions are in the making.
1.2.4 Satellite Remote Sensing
In the field of satellite images the Federal Office of
Topography together with the ETH Zurich is maintaining a
contact office (National Point of Contact) to consult and
support buyers and users of images and image data. Most
of the customers come from the universities and from the
research environment. Consulting in this context is normally
very time consuming and very seldom can the costs be
recovered. With the exception of meteorology the use of
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