The SEDRIS Data Representation Model
APPENDIX A - Classes
Spatial Index Related Geometry

Class Name: Spatial Index Related Geometry

Superclass - <Aggregate Geometry>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class specifies a spatially indexed related aggregation representing a collection of <Geometry Hierarchy> components in which each <Geometry Hierarchy> component represents a different tile within this aggregation. The <Spatial Index Data> link object corresponding to each <Geometry Hierarchy> component indicates which tile it represents.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

This class appears on only one page of the DRM class diagram.

Example

  1. Consider a <Spatial Index Related Geometry> instance with row_count = 1, column_count = 4, row_width = 1000 metres, column_width = 1000 metres. For simplicity, each of the four branches of the <Spatial Index Related Geometry> instance in this example is a <Union Of Primitive Geometry> instance as depicted in Figure 6.62.

    Spatial Index Related Organizing Principle, Example 1

    Figure 62 — <DRM Spatial Index Related Geometry> example

    Since the origin of the collection (its lower left corner, the <TM Augmented 3D Location> component) is (0, 0, 0), the coverages of the branches are:

    1. from (0, 0) to (1000, 1000)
    2. from (1000, 0) to (2000, 1000)
    3. from (2000, 0) to (3000, 1000)
    4. from (3000, 0) to (4000, 1000)

    NOTE 1  A <Spatial Index Related Geometry> instance does not specify the range of z/height/elevation values.

    Consider a triangular <Polygon> instance in branch #2 of this aggregation, with <Vertex> components having <Location> instances (1995, 0, 0), (2005, 0, 0) (2005, 10, 0).

    Since this <Polygon> instance crosses the boundary between branch #2 and branch #3, this <Spatial Index Related Geometry> instance's strict_organizing_principle is set to SE_FALSE.

  2. Consider an <Environment Root> instance representing a terrain surface that is a mix of grids and polygons, organized by spatial indexing into nine cells as depicted in Figure 6.63.

    Spatial Index Related Geometry, Example 2

    Figure 63 — <DRM Spatial Index Related Geometry> spatial indexing

    All cells except H are grids (represented in the DRM as <Property Grid> instances) captured at one level of detail. Cell H consists of <Polygon> instances as depicted in Figure 6.64.

    Spatial Index Related Geometry, Example 2

    Figure 64 — <DRM Spatial Index Related Geometry> grid and polygon example

    NOTE 2  The components of the <Spatial Index Related Geometry> instance are not ordered; the <Spatial Index Data> link objects are used to identify the individual tiles.

FAQs

What is the purpose of this class?

This class allows <Geometry Representation> instances to be organized (tiled) according to some spatial index.

Consider a data provider whose data consists of terrain <Polygon> instances that are tiled along the lines of a grid, but in which some <Polygon> instances cross over tile boundaries. Can these <Polygon> instances be organized with a <Spatial Index Related Geometry> instance?

Yes. In such a case, the strict_organizing_principle field of the <Spatial Index Related Geometry> instance is set to SE_FALSE to indicate that the indexing is not strictly followed (see examples). Each tile of the spatial index is represented by a <Geometry Hierarchy> component of S.

Where is the origin of the spatial index?

The required <Location> component of a <Spatial Index Related Geometry> instance specifies the origin of the spatial index, which is its lower left corner.

Constraints

Associated to (one-way) (inherited)

Associated by (one-way) (inherited)

Composed of (two-way) (inherited)

Composed of (two-way)

Composed of (two-way metadata) (inherited)

Component of (two-way) (inherited)

Inherited Field Elements

SE_Boolean unique_descendants; 10
SE_Boolean strict_organizing_principle; 11

Field Elements

SE_Boolean sparse; 12
SE_Integer_Positive column_count; 13
SE_Integer_Positive row_count; 14
SE_Long_Float column_width; 15
SE_Long_Float row_width; 16
SE_Spatial_Index_Spacing_Unit spacing_unit; 17

Notes

Associated to Notes


Feature_Representation

An association between a <Feature Representation> instance and a <Geometry Hierarchy> instance indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> link object on the association relationship.


Geometry_Hierarchy

An association between two <Geometry Hierarchy> instances indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> link object on the association relationship.

Associated from Notes


Feature_Representation

An association between a <Feature Representation> instance and a <Geometry Hierarchy> instance indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> link object on the association relationship.


Geometry_Hierarchy

An association between two <Geometry Hierarchy> instances indicates that the environmental object(s) that they represent have the semantic relationship indicated by the <Base Association Data> link object on the association relationship.


Hierarchy_Summary_Item

An association from a <Hierarchy Summary Item> instance to a <Geometry Hierarchy> instance indicates that the <Hierarchy Summary Item> instance summarizes that <Geometry Hierarchy> instance.


Reference_Surface

An association from a <Reference Surface> instance to a <Geometry Hierarchy> instance indicates that the <Geometry Hierarchy> instance organizes the geometric objects that specify the reference surface geometry of the <Reference Surface> instance.

Composed of Notes


Collision_Volume

In the case where multiple <Collision Volume> components are specified for the <Aggregate Geometry> instance, the union of the volumes thus specified is used in collision detection.


LSR_Transformation

An <Aggregate Geometry> instance can have an <LSR Transformation> component only when the <Aggregate Geometry> instance is within the scope of an LSR 3D SRF.

Location

The <Location> component is the origin of the collection, which is the lower left corner.

Fields Notes

unique_descendants

If the value of the unique_descendants field is SE_TRUE, each descendant of this aggregation, that is, each <Geometry Representation> instance that exists in the component tree rooted at the <Aggregate Geometry> instance shall be unique, in the sense that it shall appear in only one branch of this aggregation. If unique_descendants is SE_FALSE, at least one <Geometry Representation> instance appears in more than one branch of the aggregation.

strict_organizing_principle

If the value of the strict_organizing_principle field is SE_TRUE, each branch of this aggregation strictly complies with the organizing principle for its particular subclass. If this value is SE_FALSE, at least one branch does not strictly comply with the given organizing principle. See the organizing principle constraint for each specific subclass for details.

sparse

If the value of the sparse field is SE_FALSE, all column and row entries are present; otherwise one or more entries are not present.

column_count

The column_count field specifies the number of cells along the primary axis.

row_count

The row_count field specifies the number of cells along the secondary axis.

column_width

The column_width field specifies the length of a cell in the given unit along the primary axis.

row_width

The row_width field specifies the length of a cell in the given unit along the secondary axis.

spacing_unit

The spacing_unit field specifies the unit of measurement for column_width and row_width.


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Last updated: July 26, 2006 Copyright © 2006 SEDRIS