The SEDRIS Data Representation Model
APPENDIX A - Classes
Time Related Geometry

Class Name: Time Related Geometry

Superclass - <Aggregate Geometry>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class is an aggregation of <Geometry Hierarchy> instances, in which each branch is a representation of the same environmental entity at a different point in time, as indicated by the corresponding <Time Constraints Data> instance.

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 atmospheric forecast data organized using nested <Time Related Geometry> instances.

    Time Related Geometry, Example 1

    The <Classification Data> specify what each <Time Related Geometry> instance corresponds to. The outer <Time Related Geometry> corresponds to base forecast times, while the inner <Time Related Geometry> corresponds to forecast taus.

    In the forecast world, models are run starting at some base starting time, for example, at 0Z and 12Z. The model then produces forecasts at several deltas after the base starting time, for example, at 6, 12, 18, and 24 hours. These are known as forecast taus.

    Consequently, forecast models are run at 0Z and 12Z, and each produces a 24 hour forecast, the following overlap is obtained. 

        16 Nov                 17 Nov                     18 Nov
    0Z   +6    +12   +18   +24
               12Z   +6   +12    +18    +24
                           0Z    +6     +12    +18    +24
                                  etc.

    So to uniquely identify a forecast, the base forecast time and the delta (tau) are required. This is why nested <Time Related Geometry> has been used in this example; one <Time Related Geometry> defines the base forecast time, while its component <Time Related Geometry> defines the forecast tau.

    Note that this approach is needed only if multiple forecasts with overlapping forecasts are included in the transmittal. If instead the analysis (0Z) and +6 forecasts from each forecast are used, the following would be obtained. 

        16 Nov             17 Nov
    0Z   +6  12Z  +6   0Z   +6   12Z   +6  etc

  2. Consider a <Model> of a deciduous tree. The colour of the tree's leaves depends on the time of year, or season. Consequently, a data provider might organize a tree <Model> using a <Time Related Geometry> along the following lines. (Only the autumn representation of the <Model> is shown, but other branches are present for the other seasons).

    Time Related Geometry, Example 2

FAQs

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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; (notes)
SE_Boolean strict_organizing_principle; (notes)

Field Elements

SE_Time_Data_Type time_data_type; (notes)

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>
 instance 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> instance 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>
 instance 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> instance on the association
 relationship.

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.

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 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 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.

time_data_type

 This specifies the subclass of <Base Time Data> of which
 each <Time Constraints Data> link object in the given
 organization is to be composed.
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Last updated: July 16, 2004 Copyright © 2004 SEDRIS™