CI PA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
Figure 6: Smoothed surface with automatic generated 
NURBS patches. The black lines show the patch bound 
aries. 
point phase. It seems to be reasonable to invest that time 
into point phase because triangulation needs a well-edited 
point cloud, otherwise it is hardly possible to overcome 
the difficulties arising at polygon phase. 
5 DISCUSSION AND SUMMARY 
With the help of hybrid adjustment techniques a si 
multaneous transformation of the image and laser 
scanner data into a global co-ordinate system on the 
basis of homologous points is possible (cf. Sec. 3). 
Additionally, we used variance component analysis 
for the determination of the individual accuracies of 
the different observation types within the adjustment 
procedure. These accuracies can be compared with the 
nominal accuracy of the measurement sensors (e.g.: The 
computed variance of the range measurements to the 
signalized tie points of the fine scans is the same than the 
nominal accuracy of the laser scanner Riegl LMS-Z360.). 
Furthermore, the analysis shows that the accuracy of the 
coarse panorama scans is lower than the one of the fine 
scans and that the manual measurements in the digital 
images of the signalized tie points have sub-pixel accuracy. 
The generation of the object model of the statue 
Marc Anton was performed with the software package 
GeomagicStudio on the basis of the laser scanner point 
cloud. During the modelling process we have recognized 
that the laser scanner has obviously problems with 
measurements close to the contour of the objects (cf. Fig. 
4). This can be explained by the beam diameter and the 
fact, that only a part of the energy is reflected from the 
object surface, the other part is lost, or reflected further 
behind. As the intersection angle between the surface 
and the laser beam comes closer and closer to 180 °, the 
reflection area on the surface becomes bigger, too. This 
may also explain the deterioration of the measurement 
quality. 
In general the triangulation of the data did work 
quite well, but there occurred problems in occlusion 
areas. In these regions time consuming manual editing 
was necessary. Additionally problems were caused by 
random measurement errors (approx. ±2cm dispersion of 
the point cloud around the averaging surface). Due to 
this noise local curvature based re-sampling methods did 
fail. Therefore smoothing operations were necessary. As 
a result, the final surface model is a compromise between 
smoothness and detail preservation. The difference 
Figure 7: Color coded difference model between the final 
triangulated surface and the original laser point cloud data 
(units: m). 
between the final triangulated surface and the original 
laser scanner point cloud can be seen in the Fig. 7. The 
average distance of the points to the model is 12mm 
and the standard deviation of these differences is 13mm. 
Finally, a NURBS surface is automatically computed on 
the basis of the triangulation. This final CAD-model (cf. 
Fig. 6) describes the statue by a continuous surface (in 
the case of our statue it has holes due to missing data). 
This model is differentiable within the boundaries of one 
NURBS-patch, whereas on the patch boundaries this 
differentiability is only approximatively given (epsilon 
tolerance). 
On the basis of our experiences gained during the 
modelling step, we can say that it would be very useful to 
integrate additional image measurements into the mod 
elling process. Especially the accurate representation of 
edges on the statue would be much easier with the help of 
additional image data. As mentioned above, the distance 
measuring unit of the laser scanner has difficulties with 
measurements close to the contour of the object. It would 
be possible to eliminate this lack by the digitalisation 
of these line features in the image data. This capability 
is demonstrated in Fig. 8. For this visualization the 
contours of two lions were digitized in one image. Then 
for the determination of the 3D co-ordinates these contour 
points are projected into a vertical plane. Finally, these 
points are connected to the projection center of the digital 
image. This leads to a general cone which is displayed 
with the help of a VRML-visualization. Additionally 
to the possibility of accurate 3D point or line/curve 
measurements the image data provides texture informa 
tion, which can be very important for interpretation and 
documentation. Therefore the next aim for the docu 
mentation of such an object will be the task to project 
the texture information onto the final surface model in 
order to generate a photo-realistic 3D model of the statue. 
Summing up our experiences in the combined use of 
laserscanning and photogrammetry for heritage recording 
and documentation it turned out that both techniques 
are necessary for the determination of a high quality 3D 
model. With the help of hybrid adjustment techniques all 
observations can be simultaneously transformed into one 
global co-ordinate system ([ORPHEUS/Orient, 2003]). 
As mentioned at the beginning, the modelling of the 
statue Marc Anton is - due to its complexity - a very 
difficult task. During data capturing we had to accept 
data holes in occlusion areas to reduce the time for