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content, Level of Details (LoD), appearance information, and distribution formats.
Dietze et al. (
2007
) and Boeykens and Bogani (
2008
) also consider the geospa-
tial reference system, processing background, and data extent. All of these propo-
sitions also agree that metadata concepts should be decomposed to explicit data
fields (if possible with suggested code lists) to avoid long and textual summaries.
In the absence of a genetic 3D metadata, these propositions do not side with each
another because they are very domain and application specific according to the lev-
els of ontology dependence stated by Guarino (
1998
). For instance, Boeykens and
Bogani (
2008
) and Flotynski and Walczak (
2013
) focus on documenting 3D graph-
ics overlooking other types of 3D geospatial models such as those stored in data-
bases or defined by semantic models. One important role of metadata is to describe
the content of the respective dataset. However, the conceptual point of view of 3D
graphics is not capable of advocating the semantic aspect of 3D models because
such aspect is not part of its known concepts (Zamyadi et al.
2011
). For another
example, one may refer to various expressions of LoD as it is a key point of dis-
cussion among producers and users of 3D geospatial models (Stoter et al.
2011
).
Dietze et al. (
2007
) document LoD according to CityGML LoD while Boeykens
and Bogani (
2008
) relate LoD with number of faces and vertices. Now, compare
this to the numerous parameters which are mentioned in the literature only for
implying the geometric LoD including but not limited to point density (Emgard and
Zlatanova
2008
, Haala et al.
1998
), primitive counts (Metral et al.
2009
, Badler and
Glassner
1997
), triangle size (Cretu
2003
), pixel and voxel size (Penninga
2008
),
and single and multiple scales (Jones et al.
2009
). Furthermore, the implication
of LoD goes beyond geometry with geometric-thematic LoD in CityGML (Kolbe
2009
), attribute scale as thematic LoD (Hagedorn and Döllner
2007
), and level of
realistic visualization as graphical LoD (Badler and Glassner
1997
). An impor-
tant mismatch is with Building Information Modeling (BIM) introducing LoD as
the abbreviation of Level of Development which is the measure of how seriously
one can consider the information which is provided by a BIM element (AIA
2013
).
Meanwhile, different BIM guide lines add exclusive terms and definitions such as
Information Level of Detail (CIC
2013
) and Graded Component Creation (AEC UK
2012
) to relate the level of details with data granularity. Therefore, enhancement of
metadata profiles with a single property which documents level of details by one
exclusive definition, as suggested for CityGML LoD in the proposition of Dietze
et al. (
2007
), is insufficient for documenting the 3D geospatial models which con-
form to other specifications such as BIM. Indeed, the more general ontology level of
Guarino (
1998
) is required to achieve our goal of discoverability by mass web users.
A conclusion from the given examples is that a top-level metadata (i.e. higher
level of abstraction than domain and application specificity) is required to accom-
modate whatever ontological level by providing generic information about the
nature of 3D geospatial models. In such sense, a shortcoming of ISO 19115 is
that it does not define 3D geospatial models generically. The closest literary
indication is “
Stereo Model
” from “
Spatial Representation Type
” code list. But,
“
Stereo Model
” is defined as a “
three
-
dimensional view formed by the intersecting
homologous rays of an overlapping pair of images
” which is only specific to
