CIPA 2005 XX Internationa/ Symposium. 26 September - 01 October. 2005. Torino. Italy 
respectively, involving both information processing and 3D 
model generation. Roughly speaking, coarse level would 
correspond to piecewise-linear robust model with a low number 
of meaningful control points, whereas fine level would 
correspond to piecewise-smooth accurate model with selective 
dense clouds of points. The interplay between both of them is 
performed in terms of cascading algorithms depending on the 
adaptive behaviour to spatial complexity of captured regions. A 
3d visualization is also benefited from the two-level approach: 
coarse piecewise-linear model is the support for interactive 
display, which is extended to a fine piecewise-smooth model. 
Methodology and obtained results are illustrated with the 
surveying of a late Spanish medieval farm-castle in Trigueros 
del Valle (Valladolid, Spain), currently in excavation and 
conservation tasks. To achieve it, we have used a laser device 
ILRIS 3d (Optech). Fusion of information arising from large 
ranging scanning (arising from ILRIS 3d) and short-range 
(arising from Minolta 910) is performed on another example 
corresponding to the Capilla de San Pedro (Monasterio de 
Valbuena, Valladolid, Spain). This small chapel of the early 
gothic style, has been in excavated along the first months of 
2005; it presents several tombs, which have been scanned to 
high resolution. A more complete surveying of underground 
castle dependences is still standing. Main software tools used 
are Polyworks for processing discrete clouds of 3d points, and 
AutoCAD 15 for managing architectural primitives arising from 
the exported subclouds. 
The paper is organized as follows: Section 2 is devoted to 
explain some aspects of buildings which are relevant for 
information capture depending on the chosen framework and 
the planned application (archaeological or architectural 
surveying). Next, an outline of algorithms for the volumetric 
decomposition based in tetrahedra is provided. The fourth 
section displays the results obtained from the application of the 
performed implementation of algorithms. A comparison of 
obtained results following different methodologies is presented 
and discussed in section 5. An evaluation of results, conclusions 
and some remarks about next future work are given in the final 
section. 
2. CAPTURE 
A specific methodology for archaeological surveying has been 
developed along the last years of 20 lh century with usual 
photogrammetric resources [Miyatsuka et al, 1996], and 
including laser scanning contributions from the early years of 
21 st century [Ioannidis et al, 2000], [Agnello et al, 2003], 
[Kadobayashi et al, 2003], [Finat et al, 2005], between others. 
So, we restrict ourselves to some specific questions relative to 
surveying of an archaeological site currently in excavation. 
Military Cultural Heritage poses some specific problems for 
surveying linked to different layers, sometimes partially hidden, 
which are difficult of identifying. The castle of Trigueros del 
Valle was built along the 14 lh century with important 
modifications along 15 th and 16 lh centuries. It has a typical 
external structure including cylindrical towers along the 
fortified perimeter, two main rectangular towers as residences 
for owners and soldiers. 
Figure 1: An internal 3d scan with the court yard and the ruined 
tower of the castle of Trigueros del Valle 
The internal stmcture corresponds to an untypical farm-castle, 
with a large number of semi-subterranean dependences 
organized around an internal court yard. Uncontrolled 
excavations or partial demolitions around the underground 
dependences are in the issue of the current bad state of the 
whole building. To prevent the ruin of both rectangular towers 
several actuations on the most important tower have been 
performed with severe restorations which have avoided its total 
ruin. Deviations with respect to the vertical line of the second 
tower are important, also. Archaeological vestiges are 
ubiquitous inside the perimeter. The current architectural and 
archaeological surveying of the whole building, far from being 
simply a repository, contributes in a substantial way to the 
knowledge and understanding of the castle and landscape 
inventorying, 
Figure 2: Map with localizations of scans for the castle of 
Trigueros del Valle 
Data collection for the medieval castle of Trigueros del Valle is 
performed with the laser scan Ilris 3D (Optech) with a spot of 
between 5cm and 20 cm and a semi-metric calibrated camera 
with a scale near to 1:80 mounted on the same tripod along the 
capture for minimizing errors linked to parallax effects in 
merging views and scans. Each laser scanning provides at least 
thirty and fifty thousand points, and it is performed to have 
about an overlapping of at least 20% between adjacent scans. 
Scanner localizations and capture are limited by consolidation 
work. 
A key fact for merging is the right identification of homologue 
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