TERRESTRIAL LASERSCANNING AND PHOTOGRAMMETRY - ACQUISITION
TECHNIQUES COMPLEMENTING ONE ANOTHER
J. Jansa ?, N. Studnicka ^, G. Forkert *, A. Haring", H. Kager g
? Christian-Doppler-Laboratory "Spatial Data from Laser Scanning and Remote Sensing", Vienna University of
Technology, Austria
? Riegl Laser Measurement Systems, Horn, Lower Austria
* No Limits IT GmbH, Vienna, Austria
d Institute of Photogrammetry and Remote Sensing (LP.F.), Vienna University of Technology, Austria
Commission HI WG 7
KEYWORDS: Laser Scanning, Data Combination, Object Reconstruction, Terrestrial Mapping, Close Range, Fusion
ABSTRACT
The high spatial resolution of photogrammetric imaging
bear a great potential if combined for both data acquisition
Laboratory at LP.F. for "Spatial Data from Laser Scanning
terrestrial applications. The Austrian company NoLimits as one
NoLimits operates a City Scanner,
adjustment can be improved by up to a factor of three
demonstrate. Besides, combining both data sets presents an opportunity 0
investigation.
ZUSAMMENFASSUNG
In der hohen rüumlichen Auflósung der photogr
Raum mit Laser Scanning zu vermessen, hat
Aufnahmeverfahren genutzt werden kann. Ein Bereich des
Laserscanning und Fernerkundung" konzentriert sich auf die Nutzung
ver des Forschungslaboratoriums, verwendet diese Datenfusion in einen
egl Laser Scanner und einer digitalen Kamera. Die Genauigkeit nach
erden, wenn man beide Technologien gleichzeitig nutzt, wie erste
Anwendungen. Die ósterreichische Firma NoLimits, ein Parti
City Scanner, einer mobilen Aufnahmeeinheit mit einen Ri
einem Blockausgleich kann bis zu einem Faktor 3 verbessert w
Untersuchungen zeigen.
Objekten.
1. INTRODUCTORY NOTES
Terrestrial laser scanning has become one of the standard
technologies for object acquisition in surveying engineering.
The possibility to obtain à dense three-dimensional point cloud
of the surface of the object under investigation almost
immediately excels other common surveying techniques.
Basically two measurement principles are common: light
sectioning and triangulation; and time-of-flight measurement.
One representative of the first group is, for instance, the
Minolta VI-900, (Minolta, 2004). While this laser scanner
works well for very close-range application of no more than
several meters, terrestrial surveying in the range of above | m
up to 100s of meters is usually carried out with the help of the
second sort of instruments. Examples are Riegl’s LMS-Z4201
(Riegl, 2004) or Cyrax HDS3000 (Cyrax, 2004).
In addition, the reflectance of the surface may be measured by
recording the intensity of the reflected laser beam, although this
way of generating a grey-level image is limited to the
wavelength of the laser beam (e.g. near infrared at Riegl or
green at Cyrax). A more sophisticated technique is able to
measure true colour intensities at each laser dot location in a
separate measurement step practically simultaneously to the
distance registration. There is a certain drawback that has to be
taken into consideration: the spatial resolution of the laser
ts is limiting the practically possible resolution of
] imaging. Digital cameras could provide a higher
scanners (if economic aspects are
measuremen
conventiona
spatial resolution than laser
So nebenbei hat man eine schnelle und eindrucksv
v and the excellent capability of measuring the 3D space by laser scanning
and data compilation. One field of the Christian Doppler Research
and Remote Sensing" focuses on exploiting this potential, in particular in
of the lab's partners uses this sort of fusion for city modelling.
a mobile mapping device with Riegl scanner and digital camera. Accuracy after a block
if both technology were utilised simultaneously, as first investigations
f quick and illustrative visualisation of the objects under
ammetrischen Aufnahmetechniken und der hervorragenden Móglichkeit, den 3D
man ein Potential zur Verfügung, welches durch Kombination beider
“Christian Doppler Forschungslabors” für “Räumliche Daten aus
dieses Potential, im Besonderen für terrestrischen
olle Visualisierungsmöglichkeit von den untersuchten
taken into account) and most importantly, the relative
geometrical stability (from one point to the other) is guaranteed
by the CCD sensor matrıx, while the laser beam is individually
positioned between each measurement, representing a dynamic
principle. Therefore, current laser scanners use a combination
of the two sensors — the distance measurement unit and a
separate digital camera unit. Still, a certain shortcoming
remains: While many laser scanners can acquire data over à
(part of a) sphere, e.g. an angular range of 360? degrees
horizontally and at least 90° vertically, the cameras’ field of
view is by far smaller and the cameras have to be positioned in
several directions in order to cover the same region as the laser.
Cyrax HDS300, for instance, needs 111 individual images of
1024 x 1024 pixels for one 360° x 270° scan.
Pure photogrammetric compilations based on images usually
don’t cause many interpretation problems and also the
achievable accuracy may be rather high. Due to efficiency
considerations the 3D point density of the measurements Is
commonly low (even if automatic matching procedures are
employed) or, in case of poor or missing texture, measurements
may even fail. Both shortcomings can be overcome by laser
measurements where in turn the image contents may support the
interpretation of the range data and additionally allow the
surveying of grey or colour details of the object texture which,
of course, is not included in the range measurements. Hence, by
. more reliable and
might call this sort
"Tactile Vision".
fusing range and image data more complete
more accurate results can be expected. One
of combined data acquisition and compilation *
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