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costs for a GIS are only 5%, personnel and software
costs are 10% each, while the data acquisition is 75%
of the costs of a GIS. This demonstrates clearly, how
important is the availability of blanket coverage and
up-to-date data. To provide digital data including image
data, terrain models, and orthophotos covering the
entire area of Switzerland as standard products for a
various number of applications and users, swissair
Photo+Surveys Ltd. started the project SWISSPHOTO
in 1995. The project includes the flight and the data
processing in several processing modules.
2. DIGITAL ORTHOPHOTOS
As the first operational products of modern techniques
in digital photogrammetry, digital orthophotos are ge-
nerated in a fully automatic process. Digital orthopho-
tos provide the following advantages:
« High accuracy, stability and information density
« Short production, low cost, high efficiency
* Flexibility in the production and in derived products
* Computer supported extraction of information with
the capability of a high degree of automation
» Simple radiometric manipulation (image quality,
mosaicing, colour editing, dynamic range ad-
justment, etc.)
* [Integration of vector data and additional information
(frame, geographical names, numbers, etc.)
For the generation of digital orthophotos the following
data must be available: digital image data, orientation
parameters of the image, digital terrain model of the
area covered by the image. For scanning analog photos
high precision photogrammetric scanners, e.g. Hela-
va/Leica DSW 200, Zeiss/Intergraph PS1, which provi-
de a certain geometric and radiometric stability, or also
desktop publishing scanners using on-line calibration
procedures (Baltsavias, 1994) can be used. Depending
on the specified application, in general, resolutions
between 10 and 50 mm are used for digitisation of
photos. The interior orientation is established by mea-
suring the fiducial marks, which can be performed fully
automatically (Schickler, 1995; Lue, 1995, Kersten and
Haering, 1995). The exterior orientation parameters can
be derived in a single image by resection in space, in a
stereo model or in a photo block by aerial triangulation
as an automated process. Digital terrain models can be
derived by several methods: (a) topographical data
acquisition in the field, (b) digitisation of available
maps, (c) data acquisition on analytical plotters, (d)
digital image correlation, and (e) laser scanning
(Lindenberger, 1991). The area of the orthophoto to be
generated must be covered by a DTM. For the automa-
tic generation of digital orthophotos the geometrically
related location in the image and the radiometrically
related density value from the image will be determined
for each pixel of the orthophoto (Figure 1). In the geo-
metric rectification process the related height value of
the orthophoto pixel, which is known from the collinea-
rity equations, will be interpolated from the DTM. For
187
the radiometric rectification grey resp. colour values,
which are interpolated from neighbouring pixels in the
image, will be addressed to each orthophoto pixel. The
computation time for generating digital orthophotos
depends on the computer performance and the selected
resolution, but, in general, it takes approximately one
hour per photo.
3. PROJECT SWISSPHOTO
The project SWISSPHOTO was started in spring 1995,
in order to provide up-to-date geo-data covering the
entire area of Switzerland with aerial images. As stan-
dard products analog and digital image data, digital
terrain models, and digital orthophotos can be offered
Digital
Orthophoto
Figure 1: Principle of digital orthophoto generation
to many users from different fields.
3.1 Flight
For the project SWISSPHOTO the entire area of Swit-
zerland was flown in two phases using colour and infra-
red films simultaneously. In phase 1, the urban areas
and the northern part was flown from June to August,
while in phase 2 the southern part and the southern
valleys were flown from August until October 1995
(Figure 2). The photo scale was approximately between
1: 24 000 (non-mountainous area and valleys) and 1: 38
000 (alps). The entire photo block includes more than
7800 images for each film material. Flight and block
data are summarized in Table 1. To reduce costs for
control point signalization and determination of the 3-D
coordinates, the coordinates of the camera stations were
recorded with DGPS using one Leica GPS receiver on
the plane and up to three reference stations on the gro-
und during the flights. Additionally, 104 well distribu-
ted points of the new Swiss GPS primary network
LV'95 were signalized prior to the flight.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
