Geoscience Reference
In-Depth Information
Fig. 6
Examples
for
2.5D
representations
(hatched)
of
buildings
and
the
corresponding
ElevationReferenceValues. a general ground, b general eave, c general roof
floor above ground', 'point inside building', 'point inside cadastral parcel', and
'roof edge'. Figure
5
illustrates the most important values by giving examples.
The 2.5D representation is defined as usual: for each x/y-coordinate, there is at
most one z-value. Hence, vertical walls and overhangs are excluded. Examples for
2.5D representations are given in Fig.
6
: the roof can be represented at eaves level
by a horizontal polygon, or the roof polygon (one polygon in case of a shed roof
(a), two in case of a gabled roof) can be represented by its actual coordinates (a).
Information on the height level the geometry refers to is given again by the values
of the type ElevationReferenceValue, see Fig.
4
. In analogy to the 2D case, the
HorizontalGeometryReferenceValue can be represented. In addition, metadata on
the accuracy of the (horizontal and vertical) geometries can be stored. The 2.5D
geometry is represented by the OGC standard 'Simple Features' version 1.2
(Herring
2006
), since the 'Simple Features' ISO standard (version 1.1) (ISO TC
211
2004
) is restricted to 2D.
3.3 The Core 3D Profile
One crucial outcome of the analysis of use cases for buildings was that three-
dimensional representations are required. Corresponding applications are noise
simulation and mapping, identifications of obstacles for air traffic, to mention only
a few examples. Hence, a mandatory 3D profile Core 3D is provided by the
INSPIRE building model. This model extends the Core 2D profile by adding three-
dimensional geometrical representations (see Fig.
7
for the UML diagram of the
Core 3D profile). The well-known Boundary Representation (Foley et al.
1995
)
which represents a solid by its bounding surfaces is employed. Buildings can be
provided in different Levels-of-Detail (LoD), which correspond to specific data
collection methods as well as to a specific group of applications. The LoD and the
geometry concepts from CityGML are used, see Fig.
8
for illustrations of LoD1 to
LoD4. The geometrical representation as well as the semantic resolution becomes
more detailed with increasing LoD. Note that a building can be represented in
more than one LoD simultaneously; an application can choose the level which is
most appropriate.
