racy of the generated DTMs are dependent on the re-
solution of the digital image data, on the characteristics
of the terrain (steep, rolling, flat), on the surface of the
terrain (e.g. urban areas, forests, lakes, etc.), and on the
accuracy of the camera orientation data. Investigations
for testing the accuracy of the DTMs have been per-
formed, but results are currently not available.
3.2.4 Orthophoto generation and mosaicing
For the automatic orthophoto generation colour image
data is mainly used. The input data consists of the
image data including their support files with the orien-
tation data, DTM, the ground sampling distance (the
standard footprint is 0.75 m per pixel), and as a se-
lectable option, the perimeter of the desired area. Befo-
re starting the orthophoto generation, a dynamic range
adjustment using a modified wallis filter is performed
for each digital image in order to avoid vignetting pro-
blems in the images. This process takes more than one
hour per image, but it runs in a batch mode over night.
The images are then mosaiced together into standard
map sheets which correspond to 74 Swiss LK25000
sheets of 6 km x 8.75 km. This will create a total of ca.
1000 sheets which are stored on CD-ROMs.
3.2.5 Data management and data transfer
Currently all digital image data and ASCII files are
saved on exabyte tapes (video8) using two tape drives.
Thus, all data on the 75 GByte disk (4 x 18 GByte
disks plus 1 GByte per SUN workstation) is temporarly
used for the processing of the current projects. For data
output resp. transfer the following storage media are
available: CD-ROM, exabyte tape, optical disk and
DAT tape. Hardcopies of orthophotos can be offered on
a plotter Hewlett Packard HP750 or on an IRIS plotter.
4. SOME APPLICATIONS OF ORTHOPHOTOS
The possibilities of digital orthophoto application in a
GIS or in other fields are multiple. The most essential
applications are the use of orthophotos as background
information for the overlay of different vector data and
for digitisation of new vector data from orthophotos.
In the following several tasks for the use of digital
orthophotos are summarized (Baltsavias, 1993):
Data quality control by overlaying of vector data
Data acquisition of vector data by digitisation
* 3-D data acquisition from orthophoto and DTM by
monoplotting
Map and data revision
e Generation of orthophoto maps
e Generation of synthetic 3-D views
* Verification of changes by comparison of multi-
temporal orthophotos
* Quality control of DTMs using stereo orthophotos
Building of an orthophotos data base as land infor-
mation data base
Data fusion with other image data
In the following examples for using orthophotos in
different applications are summarized (Kersten, 1996):
(1) Surveying
* Digital revision of vector data of 1: 10000 and
1: 5000 maps
e Visual verification of castadre maps and revi-
sion of ground objects.
(2) Consolidation and property fusion
(3) Management of water resources
e Water information system for monotoring of a
drinking water protectorate with an integrated
GIS using orthophotos for the land classifica-
tion (Grenzdórffer et al., 1995)
e water sources information system
e drainage of settlements
* hydrological maps, etc.
(4) Agriculture
* Determination of agriculture contribution
areas and fruit sequence areas, revision of slo-
pe inclination (von Dániken und Blatter,
1994), etc.
(5) Planning
* Acquisition of an inventory of the nature for
communities
e Synethic 3-D views for regional planning
(6) Supply and disposal
e DOPs serve as a basis for the overlaying of
supply network (e.g. electricity, gas, water,
waste water, long-distance heating system, TV
network, etc.) in net information systems.
(7) Environment
e Mapping of the ground
e Noise protection cadastre
e Pollutant emission cadastre
e Danger cadastre
e Suspicious area cadastre, etc.
(8) Infrastructure
e Temporal orthophotos for illustration of de-
velopments in various fields, e.g. agriculture,
forestry, urban areas, leisure-time activities,
etc.
(9) Geomarketing
Digital orthophotos combined with statistical
data (e.g. population density and structure,
spending power, etc.) for the optimization of
locations of trade business, industry, (public)
services enterprise, tourism, etc.
(10) Navigation
e DOPs as a basis for vector data acquisition of
road and traffic data for building a vehicle na-
vigation system (e.g. Travel pilot Bosch)
(11) Simulation
e Simulation systems for helicopters and planes
e Simulation systems for computer animation
and video games
(12) Tourism
* Digital orthopotos as a new form of excursion
maps, city maps, tourism guides, etc.
(13) Transport
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
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