Definition

For any octant-related organization instance O, whether an <Octant Related Geometry> instance or an <Octant Related Features> instance,

1. O shall have a <Spatial Extent> component, defining the bounding volume that the octant is organizing into octants. Since a volume is being specified, this <Spatial Extent> component shall be specified in terms of <Location 3D> components.

2. Each branch of O shall comply with the following constraints.

   1. Each component representing an octant shall have a <Spatial Extent> component, specified in terms of <Location 3D> instances. In the case of octants represented by <Geometry Model Instance> instances or <Feature Model Instance> instances, the <Model> instance being referenced shall have the <Spatial Extent> instance.

   2. The <Spatial Extent> instance of an octant is distinct from those of all the sibling octants of that octant, such that they do not overlap or intersect, except that they may have a common boundary.

   3. Consider the bounding volume defined by the <Spatial Extent> component of O, as divided into eight octants of equal size in their native SRF.

3. The strict_organizing_principle and unique_descendants field values of O shall be SE_TRUE.

Rationale

1. The octant-related organization shall provide a <Spatial Extent>, so that the data provider specifies the bounding volume that the octant is dividing into octants.

2. Each component representing an octant shall specify a <Spatial Extent>, because although octants are intended to be of equal size, "size" is not invariant under coordinate transformation. The <Spatial Extent> instances are necessary to ensure that the boundaries between octants are well-defined when coordinate conversions and transformations are applied.

3. The <Spatial Extent> instances of the branches and the octants that they represent shall correspond.

4. These <Spatial Extent> instances shall be 3D, because the concept of an octant is inherently 3D.

Example

No example supplied.

FAQs

Why specify a <Spatial Extent> for each branch of an octant? Aren't the octants of equal size?

'Size' is not invariant under coordinate transformation.