Geoscience Reference
In-Depth Information
concepts, definitions, and terms which are used to describe 3D geospatial content
and to regard their influence among various communities.
Considering explicit completeness as the main criteria of conceptualization
requires accepting several challenges as
• There is no controlled vocabulary to formally represent the 3D modeling knowl-
edge. In many cases, to name a concept and the corresponding class, the range
of the possible choices is very broad. Indeed, it is important not to add to this
complexity with avoiding new terms as much as possible. However, it is some-
times inevitable to do so when aggregating detailed topics (which are usually
finely named) to unifying metadata concepts (which are newly proposed);
• Many of the concepts which are mentioned in 3D domain carry various deini-
tions which vary among different groups of users and researchers. This requires
several recursive refinements on the list, classifications, and relationships of
the identified 3D metadata requirements. In our case, the current proposal is at
its fifth version. In such sense, extensibility plays an important role for being
as generic as possible. For example, LoD is known to be subject of numerous
arguments. In such cases, the conceptualization must be as extendable as possi-
ble by aggregating detailed classes to unifying ones (instead of adding multiple
properties to one single class).
Figure
2
presents the main structure of the proposed 3D metadata with what we
called the
Metadata Target (MD_TRGT)
core class and its 20 metadata classes
grouped in three UML packages (i.e.
General
,
Complementary
, and
Availability
).
The
MD_TRGT
class represents the subject of documentation with respect to the
levels that scientific, institutional, and software rationalities constitute 3D geo-
spatial content (e.g. dataset, thematic or implicit classes or layers). Compared
with Table
1
, the proposed classes are superior in number because several topics
have been enriched with the requirements deduced from our literature review. In
Fig.
2
, the
General
and
Complementary
UML packages comprise the contextual
and structural information. The difference between the two packages is that the
General
package contains the metadata requirements we found to be endorsed by
at least half of the investigated references. The
Availability
package documents the
path from storage to delivery, outlining the repository technologies, services, and
potential information loss en route.
The next step is to enrich the main structure of the proposed 3D metadata with
further details mainly from technical resources. Figure
3
demonstrates a subset of
the current version of the
General
package where the bold classes are the ones
from Fig.
2
. Depending on their importance and specificity, the completing details
are added to the main structure of the proposed 3D metadata as either class proper-
ties with potential domain values (
enum
for enumeration in Fig.
3
) or as aggregate
and component classes. The following notes explain this step with some examples
from Fig.
3
.
Generic metadata on the notation of the 3rd dimension:
Defining the meanings
of “3” and “D” is clearly a key element to avoid confusion in the specifications of
3D geometric content (Larrivée et al.
2006
, Bédard et al,
2002
). Accordingly, the
