Property
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Description
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Class
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Superclass
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Subclass
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Definition
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An instance of this DRM class specifies a constructed, geometric
surface that is part of the environment. The <DRM Reference Surface>
instance is used to determine the elevation of conforming points in the
component tree rooted at each hierarchy instance of which it is a
component. Conforming points are either <DRM Location 2D> instances
or <DRM Location Surface> instances. A <DRM Reference Surface>
instance also specifies how the surface is used in determining the
elevation value.
An instance of <DRM Feature Hierarchy> or
<DRM Geometry Hierarchy> requires a
<DRM Reference Surface> component if
the following conditions apply:
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There are conforming points below the hierarchy.
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The conforming points are in the scope of a 3D SRF.
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The data provider wants the locations to lie on a
surface other than the last default surface. The initial
default is the designated spatial surface specified in the corresponding
srf_context_info field. If no designated spatial surface
is specified, the surface of the ORM specified for the SRF is used.
The field values of the <DRM Reference Surface> instance in
conjunction with its associated <DRM Geometry Hierarchy> instance
define a surface for determining the elevation values
for conforming points. There are several cases:
The <DRM Geometry Hierarchy> instance is a
<DRM Property Grid Hook Point> instance that has at least one
<DRM Property Grid> component G with these
qualifications:
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the <DRM Classification Data> component of G
matches the classification field
of the <DRM Reference Surface> instance,
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G has two spatial axes corresponding to the
horizontal coordinates of the SRF, and
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G has a <DRM Table Property Description>
component for height, elevation, or bathymetry.
If the <DRM Property Grid> instance meets
the above criteria, it defines a reference surface.
The <DRM Geometry Hierarchy> instance is a
<DRM Union Of Primitive Geometry> instance that
aggregates <DRM Surface Geometry> components with
<DRM Classification Data> instances matching
the classification field
of the <DRM Reference Surface> instance.
In this case, all such <DRM Surface Geometry>
components combine to form the reference surface.
The <DRM Geometry Hierarchy> instance is a
<DRM LOD Related Geometry> instance
that aggregates (directly or indirectly)
<DRM Geometry Hierarchy> instance
cases a and/or b above under an LOD branch selected by the
lod_rule field of the
<DRM Reference Surface> instance.
The <DRM LOD Related Geometry> instance
may be of type distance, index, map scale, or spatial resolution.
The branch selected by the lod_rule field
forms the reference surface.
The <DRM Geometry Hierarchy> instance
aggregates some combination of cases a, b, or c. For each such case,
the combination of the individual reference surfaces forms the
composite reference surface.
The third coordinate-component of a conforming point is determined
as specified in 4.7.3 Location.
Within the reference surface, only geometry matching
the (possibly elaborated) classification specified by the
classification
field is used.
The
multiplicity_rule
field specifies a rule to select a single point from multiple
intersections of a ray with the reference surface defined by
the instance of <DRM Reference Surface>.
The lod_rule field
specifies a rule to select one LOD branch.
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Class diagram
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Figure 6.266 —
DRM_Reference_Surface
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Inherited field elements
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Field name
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Range
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Field data type
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None |
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Field elements
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Default field values
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Default field values for DRM_Reference_Surface
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Associated to (one-way) (inherited) |
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Associated to (one-way) |
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Associated by (one-way) (inherited) |
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Associated by (one-way) |
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Associated with (two-way) (inherited) |
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Associated with (two-way) |
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Composed of (two-way) (inherited) |
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Composed of (two-way) |
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Composed of (two-way metadata) (inherited) |
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Composed of (two-way metadata) |
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Component of (two-way) (inherited) |
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Component of (two-way) |
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Constraints
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Clarifications
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1This specifies the <DRM Geometry Hierarchy> instance
containing the <DRM Surface Geometry> instances
and/or <DRM Property Grid> instances to be
used as the reference surface.
2A <DRM Reference Surface> instance has
<DRM Property Value> components only when
the classification
of the <DRM Reference Surface> requires
elaboration by <DRM Property Value> components.
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Example(s)
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Consider a <DRM Environment Root> instance ER,
having both a <DRM Union Of Geometry Hierarchy> component
UGH and a <DRM Union Of Features> component
UF.
UGH contains a <DRM Union Of Primitive Geometry>
instance UPG_1 classified as ECC_TERRAIN_ELEVATION
and containing <DRM Polygon> components that inherit the
<DRM Classification Data> instance. UPG_1 is a
polygonal representation of terrain, forming part of the
larger environmental representation ER.
UF, the feature representation of
ER, has a <DRM Reference Surface>
component that associates to UPG_1 as
depicted in Figure 6.267:
Figure 6.267 — <DRM Reference Surface> ECC_TERRAIN_ELEVATION example
Consequently, conforming points found in the component tree of
UF use the terrain polygons of
UPG_1 to resolve elevation.
Continuing the previous example, the
<DRM Union Of Geometry Hierarchy> instance UGH
under ER contains another
<DRM Union Of Primitive Geometry> instance
UPG_2 with <DRM Polygon> components
classified as ECC_INLAND_WATER_ELEVATION as depicted in
Figure 6.268.
Figure 6.268 — <DRM Reference Surface> ECC_INLAND_WATER_ELEVATION example
UF, in turn, has a <DRM Union Of Features>
component UF_2 that is classified as
ECC_ENGINEERING_BRIDGE and contains
<DRM Linear Feature> instances using
<DRM Location 2D> instances. UF_2 also has
a <DRM Reference Surface> component with
classification =
ECC_INLAND_WATER_ELEVATION and associated to
UPG_2.
Consequently, the conforming points of UF_2 have
elevation values derived for them by being evaluated against
UPG_2.
Consider a <DRM Reference Surface> instance
R for which the geometry is a
<DRM Spatial Index Related Geometry> instance
S. Each branch of S
is a polygonal representation, part of which represents
terrain surface, part roads, and part forest canopy.
R associates to S,
and its classification field =
ECC_TERRAIN_ELEVATION. The resolution process then ignores
the road and canopy polygons, but sees all the terrain polygons
regardless of which union they are in.
Consider a <DRM Linear Feature> instance L
representing a road that mostly stays on the road geometry but
sometimes strays off. L is placed in a
<DRM Union Of Features> instance aggregating a different
<DRM Reference Surface> instance R2
with associates to the same
<DRM Spatial Index Related Geometry> instance but has
classification = ECC_ROAD.
Like R, R2 associates
to S. The resolution process for
R2 sees the road <DRM Polygon>
instances and ignores the others. For <DRM Feature Node>
instances that stray off the road, the corresponding
conforming points’ rays fail to intersect any road polygon, so the
resolution process (as per case 3) applies, and the
resolution process falls back on the previous override,
which was the terrain surface.
Consider a terrain representation organized in three-minute regions that
are grouped into one-degree cells. The cells are all collected under one
<DRM Union Of Geometry Hierarchy> instance. In the same transmittal,
<DRM Feature Representation> instances and non-terrain
<DRM Geometry Representation> instances are organized under a
corresponding spatial organization. Each three-minute hierarchy has a
<DRM Reference Surface> instance associated to the
corresponding three-minute terrain region. Each one-degree hierarchy has a
<DRM Reference Surface> instance associated to the
corresponding one-degree terrain cell. Each of the highest level feature
and non-terrain geometry hierarchies has a
<DRM Reference Surface> instance associated to the
terrain <DRM Geometry Hierarchy> instance.
In this scheme, a <DRM Location 2D> instance in a
three-minute region finds its resolution surface in the corresponding
three-minute terrain region. If a <DRM Location 2D> instance
is outside its region (i.e.,
strict_organizing_principle
= FALSE),
the containing one-degree terrain cell resolves the conforming point.
If the location ray fails to intersect the one-degree terrain cell,
the full terrain <DRM Union Of Geometry Hierarchy> instance
is used. If ray / surface intersection still fails, the elevation
is resolved by the designated spatial surface.
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