Geoscience Reference
In-Depth Information
Geometric Dimension
(
GDM
) class decomposes the notion of dimension into the
following generic components that include:
• the dimension of the global universe and local referencing sub-universes (i.e.
3D or 2D or 1D where the two latter potentially exist in 3D datasets for the-
matic data such as speed limits located using linear referencing on roads and
street signs located with left/right offsets added to linear referencing);
• the dimension of the geometric primitives (i.e. 0D-3D);
• and the dimension of the model as this proposal adheres to the deinitions of
Larrivée et al. (
2006
) and Bédard et al. (
2002
) and requires to follow the pro-
posed definition of model dimension which can be either 2D
+
1D (Larrivée et
al.
2006
), 2.5D, 2.75D, 2.5D
+
3D (Penninga
2008
), and etc. or real 3D.
The notion of dimension as structured in the proposed
GDM
class is more explicit
than that of the North American Profile (NAP) of ISO 19115. In NAP metadata,
the number of dimensions is specific to grid representations (excluding vectors)
and has varying definitions as vertical axis, direction of motion, or sensor scan
line. Knowing that a large number of multi-dimensional models are not grids,
NAP's suitability is short on this issue.
Specific metadata on 3D geometric content
: The literature indicates that users
prefer to discover the 3D geospatial content which is close to their needs like
volumes in 3D geology and boundaries in 3D city visualization. The
Geometric
Data Structure
(
GDS
) class prepares the proposed 3D metadata for describ-
ing various types of 3D representations (e.g. 2D with elevation attribute, 3D
points, Interpolated surface, surface extrusion, patches, B-Rep, and voxel) in
the
Geometric Content
property. Moreover, the
GDS Object
class is an addi-
tional component to specify the comprising geometric objects (e.g. curve, tri-
angle, and solid). Unlike NAP metadata, this assembly permits distinguishing
Boundary Representation (B-Rep) solids like in CityGML from Constructive Solid
Geometry (CSG) solids like in IFC models.
Rigorous metadata on LoD
: The literature and inventory show that LoD is
expressed by various parameters which are sometimes borrowed from other appli-
cation topics. For example, the number of geometric primitives in a model is a
self-demanding parameter which also refers to LoD. Regarding the large num-
ber of statements which imply LoD, defining a generic structure to document
LoD requires starting with several detailed indicators and moving upward to
unify them. Thus, the
Level Of Detail
(
LOD
) class aggregates several parameters
from other parts of the proposed 3D metadata using explicit association classes
(e.g. the
LOD GDS Content
association class permitting several definitions based
on the
Geometric Content
property of the
GDS
class). Besides, some particular
definitions of LoD are globally accepted among specific domains (e.g. CityGML
LoD in semantic city modeling). The
LOD Particular
abstract class permits gen-
erating such definitions as sub-classes. The
LOD
class permits users to assess vari-
ous aspects of LoD in a unifying manner. For example, a 3D city model can be
documented by multiple proprietary definitions of level of details simultaneously
