The SEDRIS Data Representation Model
APPENDIX A - Classes
Property Grid

Class Name: Property Grid

Superclass - <Data Table>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class is a <Data Table> instance that has at least one but not more than three spatial axes. Spatial axes shall always appear before any other <Axis> components in the ordered list of <Axis> components for the <Property Grid> instance.

A spatial axis is an <Axis> component that describes sampling along one of the components of the SRF of the <Property Grid> instance. Hence, it is directly useful for locating the sample values in space. To qualify as spatial, the <Axis> component shall match the SRF exactly, using a consistent specification (e.g., the same ORM, direction vector and units). Spatial axes have the following characteristics.

  1. The spatial <Axis> components of a <Property Grid> instance shall always be the first members of the ordered set of <Axis> components. The spatial_axes_count field indicates how many of the <Axis> components are spatial. Because the <Axis> component ordering also determines the scanning order when data is retrieved from a <Data Table> instance, placing the spatial axes first imposes some limitations on the way data can be scanned.
  2. There are no other ordering rules for spatial <Axis> components. If a producer has a choice, it is recommended that spatial <Axis> components be ordered in the same way as the SRF components. As mentioned in the previous item, this is not always possible. Thus, no assumptions can be made about the ordering apart from those stated above.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

Example

  1. A DTED <Property Grid> instance is associated to <Areal Feature> instances representing DTED accuracy areas supplemental to the grid.

  2. Consider a <Property Grid> instance classified as ECC_WATERBODY_TEMPERATURE_PROPERTY_SET for an ocean volume. Ocean temperature features, such as warm/cold currents, fronts, and eddies, are associated to specific cells of the <Property Grid> instance.

  3. Consider a transmittal provided by a data producer whose format uses polygons rather than grids to represent terrain, where the polygons define a default post spacing. To provide this default post spacing in the transmittal, the data provider provides an empty <Property Grid> instance, attaching it to the hierarchy with a <Property Grid Hook Point> instance, as usual, with the structure depicted in Figure 6.43.

    Property Grid, Example 3

    Figure 43 — <DRM Property Grid> example

    The spatial <Axis> instances define the extents and the spacing of the <Property Grid> instance. The data provider has the option of providing <Property Characteristic> components for the <Table Property Description> instance to supply the minimum and maximum elevation values.

FAQs

Since <Property Grid> is a subclass of <Data Table>, and a <Data Table Library> instance is composed of <Data Table> instances, doesn't that mean that a <Property Grid> instance can be a component of a <Data Table Library> instance?

Yes.

What are examples of non-spatial axes?

Any <Axis> instance for which the axis_type is not spatial is a non-spatial <Axis> instance. Examples of such axis_type values are EAC_MONTH, material index, EAC_DENSITY. There are also <Axis> instances that seem to have spatial meaning but are not "spatial" to the DRM, for example, atmospheric pressure height, height above or below terrain surface, azimuth. These are non-spatial to SEDRIS because they require either additional information (such as the location of the terrain surface) or a parametric formula (such as the standard atmosphere model) to convert their values into a <Location> instance in the SRF of the <Property Grid> instance.

Why is a <Property Table> instance permitted to have other <Data Table> instances as components?

This mechanism allows a <Property Grid> instance's cell data element to specify an index into the set of ordered <Data Table> components, so that any <Data Table> component can be referenced by many data cells. See <<Index Codes within Tables>> for further details.

Why is a <Property Grid> instance allowed to associate directly with a <Feature Representation> instance? Couldn't the same functionality be achieved by associating the <Feature Representation> instance with a <Property Grid Hook Point> instance?

No. A <Property Grid Hook Point> instance may have several <Property Grid> components, making the main connection between a <Feature Representation> instance and a <Property Grid> instance ambiguous.

What if a cell in a <Property Grid> instance is related to several <Feature Representation> instances simultaneously?

This is easily handled by having the cell index to a (nested) <Data Table> component of related <Feature Representation> instance IDs (EAC_NUMERIC_OBJECT_IDENTIFIER). Such <Data Table> components of related <Feature Representation> instances shall be classified as ECC_RELATED_OBJECT_SET.

What is the point of having an "empty" <Property Grid> instance, that is, with data_present = SE_FALSE?

Because it provides an outline or template of the <Property Grid> instance's information by providing the size, orientation, spacing, and so on of the <Property Grid> instance without any cell values.

This makes it possible, for instance, for a consumer who requires <Property Grid> instances rather than <Polygon> instances for terrain to derive the <Property Grid> representation from the <Polygon> representation (see example 3).

Constraints

Associated to (one-way)

Associated by (one-way)

Composed of (two-way) (inherited)

Composed of (two-way)

Composed of (two-way metadata) (inherited)

Component of (two-way) (inherited)

Component of (two-way)

Inherited Field Elements

This class has no inherited field elements.

Field Elements

SE_Short_Integer_Positive spatial_axes_count; 4
SE_Short_Integer location_index[]; 5
SE_SRF_Context_Info srf_context_info; 6
SE_Boolean data_present; 7
SE_Boolean relative_to_hook_point; 8

Notes

Associated to Notes


Feature_Representation

An association between a <Property Grid> instance and a <Feature Representation> instance indicates that the environmental object(s) represented by the <Feature Representation> instance and the <Property Grid> instance (or some specific cell data within that <Property Grid> instance) have the semantic relationship indicated by the <Base Association Data> link object on the association relationship. Each associated <Property Grid> instance indicates whether the entire <Property Grid> instance or only some specific cell data within it is participating in the relationship in question.

Associated from Notes


Feature_Representation

An association between a <Property Grid> instance and a <Feature Representation> instance indicates that the environmental object(s) represented by the <Feature Representation> instance and the <Property Grid> instance (or some specific cell data within that <Property Grid> instance) have the semantic relationship indicated by the <Base Association Data> link object on the association relationship. Each associated <Property Grid> instance indicates whether the entire <Property Grid> instance or only some specific cell data within it is participating in the relationship in question.

Composed of Notes


Classification_Data

The <Classification Data> component indicates the kind of information represented by the <Data Table> instance, such as terrain elevation or water characteristics.

Fields Notes

spatial_axes_count

The spatial_axes_count field specifies how many axes of the <Property Grid> instance are spatial axes.

location_index

The location_index field specifies up to three grid indexes that identify the grid cell that contains the location corresponding to that specified by the <Location 3D> component of the <Property Grid Hook Point> aggregate of the <Property Grid> instance. The identified cell is where the <Location 3D> instance is attached to the <Property Grid> instance. The location_index shall specify a valid cell within the <Property Grid> instance; that is, the indexes shall be within the appropriate bounds of the <Property Grid> instance. Only the first spatial_axes_count entries of location_index are significant.

srf_context_info

The srf_context_info field specifies the SRF within which the <Property Grid> instance is defined. The griddedness of spatial positions is dependent on the properties of the SRF. Coordinate conversions and transformations are not, in general, linear, so that a set of points that form a regular array of positions in one SRF may not be regular in another SRF. Therefore, in order to preserve griddedness, a <Property Grid> instance specifies an SRF in which the data positions form a grid.

data_present

If data_present = SE_TRUE (the default), the <Property Grid> instance contains cell values that can be extracted by invoking the appropriate API functions. Otherwise, if data_present = SE_FALSE, the <Property Grid> instance does not contain any cell values although it may provide everything else that a populated <Property Grid> instance can provide.

relative_to_hook_point

The relative_to_hook_point field specifies whether the cell data of the <Property Grid> instance is specified relative to the context of a <Property Grid Hook Point> instance that references it.


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Last updated: July 26, 2006 Copyright © 2006 SEDRIS