In: Stilla U, Rottensteiner F, Paparoditis N (Eds) CMRT09. IAPRS, Vol. XXXVIII, Part 3/W4 — Paris, France, 3-4 September, 2009 
119 
them rectangular, if they are nearly squared. Both components 
use appropriate approximation algorithms and both use the geo- 
metric/topologic model part, but change only the geometry. This 
correction transfers the model of figure 4 to the one in figure 3. 
Geometry/topology supplement. Models extracted from 2d 
images are usually incomplete, since hidden information is miss 
ing. For urban data (sometimes) plausible assumptions may be 
made about the 3d-structure of the objects (e.g. they may be as 
sumed to be cuboids). 
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S CityGML WallSurface [2] 
S S| Wall surface 2 (#7) 
S CityGML Window [2] 
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B CityGML Window [2] 
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Figure 5: Geometry/topology supplement: Incomplete Example 
model (left), supplemented example model (right). 
and vice versa. The component adds openings or building to a 
city model, if their related boundary surfaces belong to this city 
model. Figure 6 shows a an example of a semantically poor 
model which is be transformed into the full model of figure 3 
by this component. The component uses the semantics and the 
geometric/topological model part, but changes only semantics. 
4.4 Model transformation 
A general class of processing activities is the modification of an 
integrated model by some kind of model transformation. There 
are geometry/topology transformations and semantic transforma 
tions. An example for geometry/topology transformation could 
be triangulation. An example for latter might be changing the 
CityGML like semantics part into one according to a proprietary 
ontology. 
4.5 Model export 
In general the integrated model or at least parts of it have to be 
stored persistently after processing. During model export an in 
tegrated model is written to a file. 
The component TgModelWriter writes a full integrated model 
to a .tg-file. If the exported .tg-model is imported again, no infor 
mation will be lost. 
During geometry/topology supplement different kinds of geomet 
ric and topological information are added to an integrated model. 
The CuboidCompleter tests if there are incomplete cuboids in 
the integrated model and completes them by adding mirrored in 
verted copies of existing 3d faces (figure 5). The component uses 
the geometric/topologic model part, and enhances geometry as 
well as topology. 
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Semantic model improvement. Given a corrected and supple 
mented model, also semantic information might be inferable and 
should be added to the model. 
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H Window 2 (#26) 
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- CityGML Door [1] 
Mi Door (#22) 
B CityGML GroundSurface [1] 
Ground surface (#12) 
S CityGML WallSurface [4] 
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li§l Wall surface 3 (#8) 
[ill Wall surface 2 (#6) 
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0 CityGML Roof Surf ace [4] 
M| Roof surface 4 (#20) 
| - / S Roof surface 3 (#18) 
a Roof surface 2 (#16) 
/ Roof surface 1 (#14) 
Figure 6: SemanticsSupplement: Model without relations be 
tween building and boundary surfaces as well as boundary sur 
faces and openings. 
During semantic model improvement different kinds of semantic 
information are added to an integrated model. The component 
SemanticsSupplementor complements an integrated model by 
adding implicit semantic dependencies as explicit relations. It 
acts on the assumption, that if an object belongs to an aggre 
gation, its parts also have to belong to this aggregation as well 
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Figure 7: Extraction of the example graph, exported to .dot for 
mat and rendered via dotty, a Graphviz tool. 
The component DotModelWriter writes an integrated model to 
a .dot-file, the standard file-format of the Graphviz 12 graph visu 
alization software (figure 7). The result can be processed further 
using Graphviz. 
The CityGMLModelWriter writes the integrated 
model via a special graph traversal algorithm as a 
CityGML[Appearance,Building,CityObjectGroup,Generics] 
model into an .xml-file. The user can influence the result by 
choosing the LOD and the kinds of textures to be written. The 
result can be processed further by other tools. For example, 
it may be rendered via any appropriate CityGML Viewer (see 
section 1.1). If the exported .xml-model is imported again, 
information might be lost, since the integrated model contains 
more information than those covered by CityGML. 12 
12 http://www.graphviz.org