2. FUNDAMENTALS OF VIRTUAL SPATIAL DATA
PRESENTATION
Basically in a MIS the Spatial position of MIS relevant points is
described by its (Cartesian) coordinates. Based on these
coordinates the traditional Geometric content of a MIS are
- numeric coordinates of object points, printed in a list or
stored on digital storage media and/or
- 2 dimensional digital or analog line maps, namely based
on vector data and/or
- . 2 dimensional image maps, based on raster data.
In addition to these traditional Geometric deliverables of a MIS
the virtually 3dimensional presentation for MIS data, as a
modern tool for improved MIS data visualization is highly
recommended.
To verify this, two images of the same object, gained from two
different viewing positions with at least approximately parallel
look directions are required.
It shall clearly be stated, the derived stereo mates can be of real
as well as of synthetic origin!
The typically appearance of a stereoscopic impression, while
viewing two corresponding stereo mates, is due to the ability of
the human 3dimensional viewing sense.
In principal a synthetic stereo mate will be obtained from a
Geometric manipulation of the original image, by adding
appropriate horizontal parallaxes values to the original
monoscopic image.
This way for a 3 dimensional presentation of MIS data is of
course open for vector as well as for raster data.
In figure 1 are presented advantages from using stereo mates for
image data visualization. In detail, as a sample, in figure 1 there
the interpretation results of different topographic features as
interpreted in original images of extremely high resolution in
comparison with digital images showing 2.5 m, 5m, 10m, 15
m, 20m and 40 m ground Pixel size. As higher the values in the
diagram, as higher the accuracy of interpretation. From the
sketch in figure 1 it is a remarkable result, the stereo mates will
highly improve the MIS data visualization in general, which is
indicated in particular for buildings and for object features
(DTM), see figure 1.
Traditionally the horizontal parallaxes values are close related
to the object space and in particular to differences in object
heights. Apart from this, the actual meaning of the horizontal
parallaxes may vary extremely due to different application
aspects of the map respectively the MIS data to be spatial
visualized. For example, the 3™ dimension in the spatial MIS
data provided, can represent variations in temperature, in the
restoration or production progress as well in frequency (of
visiting) and color (relicts), etc..
3. METHODS FOR STEREOSCOPIC VIEWING
OF MIS DATA
Independent of the nature of the horizontal parallaxes, an
attempt for a systematic investigation of the complete list of
virtually stereo aids according to the state of the art, has been
carried out.
The principles of the 3dimensional viewing technology have
been categorized according to
* methods for the spatial presentation of stereo mates projected
without contact,
* methods for the separation of spatial presented stereo mates
projected in contact and
* methods using virtually 3 D models
Sticking to appropriate virtually stereo data representation, no
part of this investigations are, e.g., methods using simple central
perspective effects and/or shadow effects, "2.5 D effects" by
permanent moving of a queue of central perspective images or
"continuous profiling", which are methods for 3D data
determination by combining a successive queue of profiles, but
not own methods for virtually 3D data presentation, similar
holds for the Moiré effect, while materialized 3D appearance,
including the 3D mirror effect and real models are no methods
for virtually but for real 3dimensional presentation.
Mapping potential of rasterimagery and photos
{for medium scale topographic mapping of rural areas)
sicreu
high
mon
good
medium |
Mapping |
Potential |
low 7 :
I]
iJ
bldg [
interpr.aid
topographic objects
| i
nhj.rivers
i
veget. buildings -
(testsite Villefranche-sur-Cher (France}}
Í
original 1:35 C00
f£ S
| 35m
14m s :
28 m Yroundpixelsize
1
#
on
#4
rpad
=
Figure 1. Results of advantages from Spatial image data interpretation
—550—
I2 ol