-50- 
5.2 NURBS 
When NURBS modeling of a surface is chosen, the parameters 
of spline type curves are used to describe the surface instead of 
discrete mesh points. This can reduce data storage space con 
siderably. Also, when the surface is known to be smooth, the 
use of NURBS modeling can remove the noise resulting from 
scanning. NURBS modeling is supplied with some software 
packages for 3D modeling and even with some packages 
developed for handling 3D scanner data. It seems to be very 
useful for relatively small technical parts (e.g. a car fender) but 
there is a limit presently to the number of points resp. curves it 
can handle in the case of large, complex objects. 
5.3 Texture and image mapping 
Texture mapping. It is the texture only that makes any visuali 
zation of surfaces possible. The most simple case, a white textu 
re, may give the object an appearance like alabaster. This 
applies only, however, if one or more light sources are defined 
for a virtual illumination. Also, the reflectivity properties 
(relation between direct and diffuse reflection) of the materials 
have to be defined, which will result in a rougher or glossier 
surface appearance. More complex textures and more sophisti 
cated illumination procedures may be supplied with the 
scanning software, Stand-alone 3D modeling software may be 
used as well - if it can handle the large and complex objects that 
are common in cultural heritage. 
Image mapping from scanner data. Image information may 
be provided by the scanning process. In the case of ranging 
scanners, an attribute representing the strength of the returned 
signal may be available. If normalized (considering the effects 
of different range and different incident angles), this value can 
be used to create a gray tone image of the object. The cameras 
of triangulation scanners can supply a similar information or 
even record an image of the whole field of view. In most cases, 
these simple devices do not supply images of the high quality 
desired for a documentation task, however. 
Image mapping from separate cameras. For high image 
quality, especially for color images, it is advisable to use 
separate cameras (digital or film) to produce the images for 
mapping. Camera locations close to the scanner locations facili 
tate the mapping process. Orientation parameters (location, 
rotations), approximate values at least, should also be recorded 
on site. Illumination should be as uniform as possible (which is 
easy to demand but hard to achieve). 
Image projection and mosaicking. The images have to be re 
projected onto the object. Although software is available for 
placing images on the object using identical points “without in 
volving any photogrammetry”, the result may be achieved faster 
(and with a better geometric quality anyhow) if photogram- 
metric techniques (calibrated cameras, orientation parameters 
from bundle adjustments) are used. As compared to mosaics for 
topographic applications, the process for true 3D objects is by 
far more complicated. This may involve, for example, a new 
process for every small surface element to decide (based on the 
incidence angle) from which of the available images the infor 
mation has to be taken (Visnovcova et. al., 2001). Radiometric 
corrections regarding brightness, contrast and color balance 
may also be very difficult to apply since illumination conditions 
during image acquisition will never meet the pre-condition of 
being the same on every surface element of the object. There is 
no need to add, that image mapping is a very troublesome 
procedure and that there remains a large list of wishes for the 
software developers to be met (Marbs, 2002). This leads again 
to the question if the necessary professional and economical 
resources can be supplied by the scanner producers, by small 
companies specializing in this field, or by the large software 
houses involved in CAD and 3D modeling. 
6. SOFTWARE FOR DATA AND PROJECT 
MANAGEMENT 
6.1 Data tracking and quality control 
Many processing steps may be necessary to come from a set of 
point clouds and additional data such as surveying results or 
images to a final 3D representation. During these steps, 
observations are altered, adjusted, or deleted. Records should be 
kept documenting all actions applied during the project. 
Wherever adjustment processes are involved, statistical values, 
such as standard deviations and residuals, should be supplied. 
Graphical tools to visualize the differences between the original 
point cloud and the final model are of special importance for a 
final quality assessment. 
6.2 Data import and export 
Scan data. Every processing software should be able to import 
measurements taken by various scanners. This is an obvious 
condition for stand-alone software products. If software from 
scanner manufacturers is used, there might be a demand, too, to 
use it for other scanners, especially when data from different 
types of scanners (e. g. providing different resolutions) has to 
be integrated. The Cartesian coordinates of scanned points are 
not sufficient as a data interface since they do not contain 
information about the distance and the direction from where a 
point was scanned. This information may be important in 
subsequent operations such as cleaning, thinning, meshing and 
image mapping (Marbs, 2002). 
CAD and 3D modeling software. Since results have to be 
exported to CAD and 3D modeling software for further 
processing and/or storage, it is necessary to have export tools 
available which are suitable for the most common systems. 
Often, scanning results have to be compared against existing 
data models. This would also call for appropriate import tools if 
the comparison is to take place using the scanning software. 
7. AVAILABLE SOFTWARE PRODUCTS 
As shown above, “3D scanning software” actually means an ex 
tensive collection of modules for very different purposes. Some 
are specific to a certain scanner, some to 3D scanning in gene 
ral, some are tools that are needed for any kind of 3D modeling. 
Presently, all producers of 3D scanners (list see Boehler, Marbs, 
2002, or WWW, 2002) supply a selection of modules. None can 
be regarded as complete and satisfactory. Since the demand is 
obvious and the market is growing, some stand-alone software 
products for 3D scanning are available, too (table 1). 
It seems to be inevitable, however, that a certain consolidation 
will take place since the market is growing indeed, but not large 
enough for two dozen of competitors. Large CAD and 3D 
modeling software houses may also compete in this market if 
they succeed to upgrade the performance of their products for 
the import and handling of large numbers of points.