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 an aggregation of <Geometry Hierarchy> objects in which each component <Geometry Hierarchy> represents a different tile within a spatially indexed (tiled) organization of <Primitive Geometry> objects within a SEDRIS transmittal. The <Spatial Index Data> link object attached to each component <Geometry Hierarchy> indicates the tile that 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. See <<Spatial Index Organizing Principle>>, example #1.

  2. Consider an <Environment Root> describing a terrain surface that is a mix of grids and polygons, organized by spatial indexing into 9 cells.

    A B C
    D E F
    G H I

    All cells except H are grids (represented in SEDRIS as <Property Grid> instances) captured at 1 level of detail. Cell H consists of <Polygon> instances.

    Spatial Index Related Geometry, Example 1

    Please note that the components of the <Spatial Index Related Geometry> are not ordered; the <Spatial Index Data> is used to identify the individual tiles.

FAQs

What is the purpose of this class?

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

My data consists of terrain <Polygons> that are tiled along the lines of a grid, but some <Polygons> here and there cross over tile boundaries. Can I organize these <Polygons> with a <Spatial Index Related Geometry>?

Yes, if its strict_organizing_principle is set to SE_FALSE to indicate that the indexing is not strictly followed (see <<Spatial Index Related Organizing Principle>>, example #1). Each tile of the spatial index would be represented by a <Geometry Hierarchy> component of the <Spatial Index Related Geometry>.

Where is the origin of the spatial index?

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

Constraints

Associated by (one-way)(inherited)

Associated with (two-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; (notes)
SE_Boolean strict_organizing_principle; (notes)

Field Elements

SE_Boolean sparse; (notes)
SE_Integer_Positive column_count;
SE_Integer_Positive row_count;
SE_Long_Float column_width; (notes)
SE_Long_Float row_width; (notes)
SE_Spatial_Index_Spacing_Unit spacing_unit;

Notes

Associated with Notes


Feature

 An association between a <Geometry Hierarchy> instance and a
 <Feature> instance indicates that the <Geometry Hierarchy>
 and the <Feature> are alternate representations of the same
 environmental object.

Geometry_Hierarchy

 An association between two <Geometry Hierarchy> instances
 indicates that they are alternate representations of the same
 environmental object.

Hierarchy_Summary_Item

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

Reference_Surface

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

Composed of Notes


Collision_Volume

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

Location

 This is the origin of the collection, which is the lower-left corner.

Fields Notes


unique_descendants

 If this value is SE_TRUE, each 'descendant' of this aggregation -
 that is, each <Geometry> instance that exists in the component tree
 rooted at the given <Aggregate Geometry> - 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> instance
 appears in more than one 'branch' of the aggregation.

strict_organizing_principle

 If this value 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 this value is SE_FALSE, all column and row entries are present;
 otherwise one or more entries are not present.

column_width

 This is the length of a cell in the given unit along the X axis.

row_width

 This is the length of a cell in the given unit along the Y axis.
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Last updated: May 15, 2003 Copyright © 2003 SEDRIS™