central applications with a total of 90 GByte capacity
enable the storage of all types of required data. Local
connected disks with a total of about 80GByte storage
capacity enable a fast planning. Different plotting systems
(laser, electrostatic (up to AO), inkjet) are used for
visualization purposes.
For controlling and updating the 3D building data a
SPARCstation 20 with 2 60 MHZ SuperSPARC processors
is used. 128 Mbyte of random access memory and for
visualization a 24 bit graphic accelerator board and a 19"
color display are available. For local storage a total of 27
Gbyte disk capacity can be used. The stereo environment
is realized by connecting the StereoGraphics Crystal
Eyes™ system containing an infrared emitter, stereo
glasses and a controller.
For the various geographic applications the image
processing and, GIS tool ERDAS Imagine is used. In
addition a perspective view module and a vector module
(subset of the ARC/INFO package) are utilized.
Furthermore the Geographic Resources Analysis Support
System (GRASS) is used. GRASS is a public domain,
image processing and GIS package, written in C and
developed by the U.S. army. It contains powerful raster
functions and some vector functionality. The open software,
that means all sourcecode is available, enables
modification of the functions for the user-defined
specifications.
The photogrammetric applications can be done by the
OrthoMAX software package. It is a high performance
softcopy terrain mapping and geopositioning package
developed by Vision International, a division of Autometric,
Inc.. The system provides capabilities of triangulation,
stereoscopic viewing and mensuration, digital terrain
model (DTM) extraction and editing and ortho rectification.
The package is integrated into the ERDAS environment.
4. CONTROLLING THE DATASETS
3D building datasets of several German cities have been
generated with the use of analytical and digital
photogrammetric techniques by different companies. Due
to the size of these areas (1000 km?) and the density of
buildings with different shapes (especially in the downtown
areas) the controlling of the generated data is a major
problem and can not be solved completely with manual
methods. For this reason several control procedures have
been developed. These procedures have to accomplish
four major tasks:
- completness of the data
- position accuracy
- height accuracy and
- degree of specification (details of buildings)
4.1 Using GIS-techniques
In a pre-controlling process some special functions of the
GIS package GRASS are used. These functions are usefull
in finding rough errors. Instead of using a normal color
ramp in displaying the data sets (fig. 3), the building
dataset is displayed by a randomized color table. As can be
seen in fig. 4 an unexpected edge can easily be detected
by this visual method.
Fig. 3: Part of a digital city structure
Fig. 4: Randomized color display of the same part
4.2 The digital photogrammetric workstation
For further controlling the image processing system
ERDAS including the photogrammetric software
ORTHOMAX is installed.
To check the completeness of the building layers initially an
ortho-photo is made with the help of the digital area model
from the aerial photograph. This dataset is projected to the
building layers with a special overlay technique available in
the ERDAS programme. With this blend and fade function
it is posssible to accurately check whether the building
location is correct.
Apart from the building datasets which are available in a 5
m raster, a vector dataset is created which should provide
an area accuracy of 1 m. It is possible to check the site
accuracy of individual buildings by overlaying the
orthophotos with the vectors.
184
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
Wh
hei
dec
tha
be
the
obj
Int
est
ort!
vis!
The
ma
to I
this
Ho
det
4.3
The
ach
ane
con
ste
ane
run
aut
witl
adj
deti
bot
(coi
on
dat:
sigr
Wit
buil
the
eng
me:
ont
the
rast
Due
obj:
este
indi
con
prol
bec
cha
ana
tha
este
the
suff
Tot
stat
