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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004
The laser scanner is designed for non-tactile, high performance
measurements and stands out for high robustness and accuracy.
This is necessary for exploration by surveying industrial plants
and production halls, as long down times in production have to
be avoided: but it is also required for cultural sites like churches
or castles where people visiting the site should not be disturbed.
Due to the large field of view of the scanner, 360? horizontally
(azimuth) and 310° vertically (clevation), the scene to be
modelled has to be surveyed only from a few points of view.
Beside the 2D reflectance information the laser scanner
provides 3D range information in addition. Both information —
reflectance and 3D range information — correspond to each
pixel one to one. So by extracting features in an accurate way,
the combination of image processing methods and 3D geometric
information is possible.
The system itself has different scanning modes, which differ in
the spatial point distance. The mode can be selected according
to the requirements and application from Super High Resolution
(20,000 pixel per 360° horizontally and vertically) to Preview
(1,250 pixel per 360° horizontally and vertically) mode.
The acquisition time is very short: The mode for example,
which is most popular in industrial environment applications
(10,000 points horizontally and vertically) takes just 3.20
minutes for a full 360° scan.
Another big advantage of laser scanning technology is that you
can operate in total darkness as well as in daylight. This
facilitates measurement as no additional illumination is needed.
LE 7
Figure 2: The figure shows Z+F Viewer’s desktop.
SOFTWARE
There are two software tools, which were specially developed
and optimised for the IMAGER 5003: The Z+F Viewer is the
basic software for operating the scanner and performing simple
measurement (asks. Based on this the LFM builds up: This
software enables the conversion from 3D point clouds into
CAD objects and offers a comfortable interface to standard
CAD programs of more than 250 scans (10,000 x 10,000 pixel)
through a database.
Z+F Viewer
The operator software is designed for scanning in the field (see
Figure 2). The software is very easy to handle by using
predefined settings for the scanning. This allows the operator to
select between five predefined buttons for setting the
application specific scanner parameters. By selecting the
preview mode — enabling more than 12 million points to be
scanned in less than 20s — a preview of the area to be scanned in
detail can be measured and afterwards selected to be rescanned
using a higher point density.
The Operator integrates the software package Z+F Viewer for
visualisation purposes and online data measurements by means
of a so called "virtual surveying" functionality.
Directly after measuring. the first results can be seen on the
computer: Usually the reflectance image is used to get a
photorealistic impression of the scanned area. It is similar to a
black-and-white photograph and therefore does not require
much experience for interpretation.
After each scan, the surveyor can see the objects which have
been captured directly in the reflectance image (Figure 3).
When objects are hidden by other objects, it may be necessary
to rescan this region from a different point of view.
Another way of checking the scan is through the grey-coded
range image. It is the complimentary image to Figure 3, viewing
the same area: but range is displayed rather than reflectance. In
the range image, every range has its own grey level; the greater
the distance to an object. the lighter the object is represented.
Objects which are near by the sensor are almost black. As this is
not natural to the human eye, some experience is needed to gain
useful information from this view. The range image is important
for the control of the ambiguity interval, as the operator can
easily see which objects are far away and therefore are
measured with a lower point density. This image can also help
= the user to decide where exactly to take the next scan.
Figure 3: The figure shows a reflectance image. There is a one
to one correspondance between the reflectance image
and its complimentary image, the range image.
To get an overall view of the scanned area, the 3D window is
essential (Figure 4). All measured points are transformed to 3D
so that the whole point cloud is shown as a three dimensional
image which gives a good impression of the scanned region.
The user can turn the object and zoom in and out to see the
object from any point of view. Like in the reflectance image, in
this view hidden areas can be detected easily.
Simple measuring features allow the user to get the most
important measures on site and a fecling for the dimensions.
