Lehrveranstaltungsinhalt aus - Institute for Computer Graphics and ...

0.14. THE ROLE OF THE INTERNET 19
the strips need to be merged and how any discrepancies between those strips, particularly in their
overlaps, need to be removed by some computational measure. In addition, one needs to know
points on the ground with their true coordinates in order to remove any uncertainties that may exist
from the airplane observations. So finally we have a matched, merged, cleaned-up data set and we
now can do the same thing that we did with the DEM from aerial photography, namely we merge
the elevation data obtained from the laser scanner with potentially simultaneously collected video
imagery, also taken from that same airplane: We obtain a laser scan and phototexture product.
0.14 The Role of the Internet
It is of increasing interest to look at a model of a city from remote locations. An example is the
so-called “armchair tourism”, vacation planning and such. Slide 0.152 is an example of work done
for a regional Styrian tourism group. They contracted to have a mountain-biking trail advertised
on the Internet using a VRML model of the terrain. Shown is in Slide 0.153 a map near Bad
Mitterndorf in Styria and a vertical view of a mountain-biking trail. Slide 0.154 is a perspective
view of that mountain-bike trail super-imposed onto a digital elevation model that is augmented
by photographic texture obtained from a satellite. This is actually available today via the Internet.
The challenge is to compress the data without significant loss of information and to offer that
information via the Internet at attractive real-time rates. Again Diploma and Doctoral thesis
topics could address the Internet and how it can help to transport more information faster and in
more detail and of course in all three dimensions.
Another example of the same idea is an advertisement for the Grazer Congress on the Internet.
The Grazer Congress’s inside was to be viewable to far away potential organizers of conferences.
They obtain a VRML view of the various inside spaces. Because of the need to compress those
spaces, the data are geometrically very simple, but they carry the actual photographic texture
that is available through photographs taken at the inside of the Grazer Congress.
The Internet is a source of a great variety of image information, an interesting variation of the city
models relates to the so-called “orthophoto”, namely photographs taken from the air or from space
that are geometrically corrected to take on the geometry of a map. The example of Slide 0.158
shows the downtown of Washington D.C. with the U.S. Capitol (where the parliament resides).
This particular web site is called “City Scenes”.
0.15 Two Systems for Smart Imaging
We already talked about imaging by regular cameras, by radar or non-imaging sensing and by
laser. Let’s go a step further: specific smart sensing developed for city mapping. As part of a
doctoral thesis in Graz a system was developed to be carried on the roof of a car with a number
of cameras that allow one to reconstruct the facades of buildings in the city. Images are produced
by driving with this system along those buildings. At the core of the system is a so-called linear
detector array consisting of 6,000 CCD elements in color. These elements are combined with two
or three optical systems, so that 3,000 elements are exposed through one lens and another 3,000
elements through another lens. By properly arranging the lenses and the CCDs one obtains a
system, whereby one lens collects a straight line of the facade looking forward and the other lens
collects a straight line either looking backwards or looking perpendicular at the building.
In Slide 0.163 we see the car with the camera-rig driving by a few buildings in Graz- Kopernikusgasse.
Slide 0.164 shows two images with various details from those images in Slide 0.165, in
particular images collected of the Krones-Hauptschule. Simultaneously with the linear detector
array collecting images line by line as the car moves forward (this is also called “push broom
imaging”), one can take images with a square array camera. So we have the lower resolution