Table 6.274 — DRM_Time_Related_Geometry

Property

Description

Class
  • <DRM Time Related Geometry>

Superclass

Subclass
  • None.

Definition

An instance of this DRM class is an aggregation of <DRM 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 <DRM Time Constraints Data> instance.

Class diagram

Figure 6.328 — DRM_Time_Related_Geometry

Inherited field elements

Field name

Range

Field data type

unique_descendants1

 

Boolean

strict_organizing_principle2

 

Boolean

Field elements

Field name

Range

Field data type

time_data_type

 

Time_Data_Type

Associated to (one-way) (inherited)
  • None.

Associated to (one-way)
  • None.

Associated by (one-way) (inherited)

Associated by (one-way)
  • None.

Associated with (two-way) (inherited)

Associated with (two-way)
  • None.

Composed of (two-way) (inherited)

Composed of (two-way)

Composed of (two-way metadata) (inherited)

Composed of (two-way metadata)
  • None.

Component of (two-way) (inherited)

Component of (two-way)
  • None.

Constraints

Clarifications

1 If this value is TRUE, each “descendant” of this aggregation - that is, each <DRM Geometry> instance that exists in the component tree rooted at the given <DRM Aggregate Geometry> - shall be unique, in the sense that it shall appear in only one “branch” of this aggregation. If unique_descendants is FALSE, at least one <DRM Geometry> instance appears in more than one “branch” of the aggregation.

2 If this value is TRUE, each “branch” of this aggregation strictly complies with the organizing principle for its particular subclass. If this value is 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.

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

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

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

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

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

Example(s)

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

    Time Related Geometry, Example 1

    Figure 6.329 — <DRM Time Related Geometry> example

    The <DRM Classification Data> specify what each <DRM Time Related Geometry> instance corresponds to. The outer <DRM Time Related Geometry> corresponds to base forecast times, while the inner <DRM 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 <DRM Time Related Geometry> has been used in this example; one <DRM Time Related Geometry> defines the base forecast time, while its component <DRM 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

  • Consider a <DRM 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 <DRM Model> using a <DRM Time Related Geometry> along the following lines. (Only the autumn representation of the <DRM Model> is shown, but other branches are present for the other seasons).

    Time Related Geometry, Example 2

    Figure 6.330 — <DRM Time Related Geometry> example