Table 6.191 — DRM_Property_Grid

Property

Description

Class
  • <DRM Property Grid>

Superclass

Subclass
  • None.

Definition

An instance of this DRM class is a <DRM Data Table> that has at least one (1) but not more than three (3) spatial axes, which always appear before any other <DRM Axis> instances in its ordered <DRM Axis> list.

A spatial axis is an <DRM Axis> instance that describes sampling along one of the components of the spatial reference frame of the <DRM Property Grid>; hence it is directly useful for locating the sample values in space. To qualify as spatial, the <DRM Axis> shall match the spatial reference frame exactly, using using a consistent specification (e.g., the same ORM, direction vector and (possibly scaled) units.

  • The “spatial” <DRM Axis> instances of a <DRM Property Grid> shall always be the first members of the ordered set of <DRM Axis> components. The spatial_axes_count field indicates how many of the <DRM Axis> instances are “spatial”. Note: because the <DRM Axis> ordering also determines the “scanning” order when data is retrieved from a <DRM Data Table>, placing the spatial axes first imposes some limitations on the way data can be scanned, and may require reordering either by the preparer or the consumer to achieve a scanning that is more “natural” to them.

  • There are no other ordering rules for spatial <DRM Axis> instances. If a producer has a choice, it is a good idea to order spatial <DRM Axis> components in the same way as the spatial reference frame components, but as mentioned in point 1), this is not always possible, so consumers cannot make assumptions about the ordering apart from those stated above.

Class diagram

Figure 6.221 — DRM_Property_Grid

Inherited field elements

Field name

Range

Field data type

None

    

Field elements

Field name

Range

Field data type

spatial_axes_count1

 

Short_Integer_Positive

location_index2

 

Short_Integer[3]

srf_info3

 

SRF_Info

data_present4

 

Boolean

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

Associated to (one-way)
  • None.

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

Associated by (one-way)
  • None.

Associated with (two-way) (inherited)
  • None.

Associated with (two-way)

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)

Constraints

Clarifications

1 This indicates how many axes of the given <DRM Property Grid> instance are spatial axes.

2 This specifies up to three grid indices that identify the grid cell that contains the location corresponding to that specified by the <DRM 3D Location> component of the <DRM Property Grid Hook Point> aggregate of the given <DRM Property Grid> instance.

The identified cell is the attachment cell of the given <DRM Property Grid> instance; it is where the <DRM 3D Location> instance is attached to the <DRM Property Grid> instance.

The location_index shall specify a valid cell within the given <DRM Property Grid> instance; that is, the indices shall be within the appropriate bounds of the <DRM Property Grid> instance. Only the first spatial_axes_count entries of location_index are significant.

3 This specifies the spatial reference frame within which the given <DRM Property Grid> instance is defined, rather than attempting to depend on the spatial reference frame of the context in which the instance appears.

The “griddedness” of spatial positions is dependent on the properties of the spatial reference frame. Coordinate conversions and transformations are not, in general, linear, so that a set of points that form a regular array of positions in one spatial reference frame may not be regular in another spatial reference frame. Therefore, in order to preserve “griddedness”, a <DRM Property Grid> specifies a spatial reference frame in which the data positions form a grid.

4 If data_present = TRUE (the default), the given <DRM Property Grid> instance contains cell values that can be extracted via the appropriate Level 0 API calls.

Otherwise, if data_present = FALSE, the given <DRM Property Grid> instance does not contain any cell values, although it may provide everything else that a populated <DRM Property Grid> instance could provide.

5 This indicates the kind of information represented by the <DRM Data Table>, such as terrain elevation or water characteristics.

Example(s)

  • A DTED <DRM Property Grid> associated to <DRM Areal Feature> instances representing DTED accuracy areas supplemental to the grid.

  • Consider a <DRM Property Grid> instance classified as ECC_WATER_BODY_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 <DRM Property Grid>.

  • 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 would provide an “empty” <DRM Property Grid> instance, attaching it to the hierarchy with a <DRM Property Grid Hook Point> instance, as usual, with the following structure.

    Property Grid, Example 3

    Figure 6.222 — <DRM Property Grid> example

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