Class Name: Environment Root

Superclass - SEDRIS Abstract Base

Definition

The aggregating object for the Feature Hierarchy and/or Geometry Hierarchy that represent the instantiation of a collection of all data in a common spatial reference frame in a given transmittal. In other words, an Environment Root is the starting point for all objects in the same spatial reference frame in a transmittal.

Primary Page in DRM Diagram:

• 1

Secondary Pages in DRM Diagram:

• 3
• 8
• 16

Example

1. Earth.
2. An area of North America that straddles two UTM zones. The Transmittal Root would have two Environment Root components, one for each of the two UTM zones.

FAQs

Is an Environment Root required in a transmittal?

No. A valid transmittal may contain libraries, e.g. a Model Library without an Environment Root.

Can I have multiple Environment Roots in a transmittal?

Yes, provided that each Environment Root distinct values for the srf_params field (in accordance with the constraint: Environment Root Spatial Reference Frame). See example 2.

Why can Environment Root only have 0-2 Hierarchy Summary Item components?

An Environment Root does not have to have a hierarchy summary (i.e. 0). If the data producer wants to provide a summary of hierarchy information, then a can have one summary for Geometry (i.e. 1), one summary for Features (i.e. 1), or a summary of each (i.e. 2).

Can Environment Root have both Hierarchy Summary Item and Primitive Summary Item components (as opposed to either/or)?

Yes.

Can Level 0 feature topology be represented in SEDRIS?

Yes. Although in VPF, for example, the mere presence of Connected Nodes implies Level 1 topology, this is not the case in SEDRIS. The SDRM requires Feature Nodes to exist to contain the endpoint coordinates of Feature Edges. Consequently, the presence of Feature Nodes means nothing by itself. If, within a single topological layer, any two different Feature Nodes have the same Location coordinates, the topology level is Level 0. If no two Feature Nodes have identical Location coordinates, the topology level is (at least) Level 1.

Which objects (and relationships) are required to exist at each feature topology level?

At Level 0, unless the data consists solely of isolated (i.e., entity) Feature Nodes, the following objects (and the relationships among them) are all required to exist:

• Feature Edge
• Feature Edge Starting Node
• Feature Edge Ending Node
• Feature Node
• Connected Feature Edge

All other types of feature topology objects and relationships MAY also exist at Level 0, but the requirements of Level 1 are NOT met.

At Level 1, no additional objects or relationships are required. However, each Feature Node must have a unique Location (i.e., two or more Feature Nodes cannot be colocated).

At Level 2, no additional objects or relationships are required. However, Feature Edges may not intersect or overlap one another, except where they meet at a common Feature Node.

At Level 3, the remaining objects and relationships are required to exist:

• Feature Face (Regular and Universal)
• Feature Face Ring (External and Internal)
• Bordered Feature Face
• Contained Feature Node
• Contained Within Feature Face

The set of Feature Faces must be exclusive and exhaustive, forming a complete surface (i.e., Feature Faces may not intersect or overlap one another, except where they meet at a common Feature Edge). Exactly two Feature Faces border each Feature Edge.

At Level 4, Location 3Ds are required, and there must be at least one case where more than two Feature Faces meet at a single Feature Edge.

Constraints

• Environment Root Spatial Reference Frame
• Hierarchy Summary Item For Environment Root and Models
• Non Empty Environment Root

Composed of (one-way)

• optionally, some Base Time Data (notes)
• one Spatial Domain (notes)

Composed of (two-way)

• optionally, a Feature Hierarchy
• optionally, a Geometry Hierarchy
• a bounded set of Hierarchy Summary Items[0..2] (notes)
• optionally, an Interface Template
• optionally, some Primitive Summary Items

Composed of (one-way metadata)

• optionally, an Access
• optionally, some Browse Graphics
• optionally, a Citation
• optionally, some Cross References
• optionally, a Data Quality
• optionally, a Description
• optionally, a Keywords
• optionally, a Point of Contact

Component of (two-way)

• one Transmittal Root

Field Elements

Notes

Composed of Notes

Base_Time_Data

 If different than the <Transmittal Root>'s <Base Time Data>

Hierarchy_Summary_Item

 No hierarchy summary, <Geometry Hierarchy> summary,
 <Feature Hierarchy> summary, or both

Spatial_Domain

 The spatial extent of the <Environment Root> - defines the maximum
 spatial extents of the component objects