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The SEDRIS Data Representation Model
APPENDIX A - Classes Spatial Index Related Feature Topology |
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An instance of this DRM class specifies a spatially indexed related aggregation representing a collection of primitive <Feature Topology> instances.
An <Aggregate Feature> instance can have more than one spatial related organization for its topology. In a given transmittal, the top <Aggregate Feature> instance under an <Environment Root> instance has a single 10 kilometre by 10 kilometre spatial related organization of topology spanning the entire transmittal, as well as a single 500 metres by 500 metres spatial related organization of topology also spanning the entire transmittal. That top <Aggregate Feature> instance has two <Spatial Index Related Feature Topology> components, one for the 10 kilometre squares and one for the 500 metre squares.
We need a 'branch', and each branch from an aggregation is a hierarchy object, because <Aggregate Feature> instances contain <Feature Hierarchy> instances. When an <Aggregate Feature> instance has a <Feature Topology Hierarchy>, that <Aggregate Feature> represents a distinct topological surface. We shall organize a topological surface, a.k.a. an "independent topology", which eventually, in the DRM, is 'rooted at' a single <Aggregate Feature> instance.
The <Feature Hierarchy> instances are either <Aggregate Feature>s or <Feature Model Instance>s. The topological organization of the <Model>, if any, is contained within the <Model>, so we're left with a need to specify the topological organization of an <Aggregate Feature> instance. The organizing principle shall be applied at the <Aggregate Feature> instance level - no lower, no higher.
The same spatial indexing structure can be shared by multiple <Aggregate Feature> instances, because there can exist multiple organizations of the same set of <Feature Representation> instances. When a single set of <Feature Representation> instances is organized by multiple classification approaches, it is still the same set of <Feature Representation> instances being dealt with, and still the same set of <Feature Node> instances, <Feature Edge> instances, and <Feature Face> instances. Changing the logical organization of the <Feature Representation> instances has no effect on the spatial organization of the underlying topological primitives. Thus, one spatial organization for a set of topological primitives may be shared by many different organizations (aggregations) of <Feature Representation> instances, where the <Feature Representation> instances are composed of the same spatially organized topological primitives, regardless of the organization from which the <Feature Representation> instances are viewed.
The feature_topology_level field specifies the level of feature topology that is present within the hierarchy represented by the <Feature Topology Hierarchy> instance.
If the value of the sparse field is SE_FALSE, all column and row entries are present; otherwise one or more entries are not present.
The column_count field specifies the number of cells along the primary axis.
The row_count field specifies the number of cells along the secondary axis.
The column_width field specifies the length of a cell in the given unit along the primary axis.
The row_width field specifies the length of a cell in the given unit along the secondary axis.
The spacing_unit field specifies the unit of measurement for column_width and row_width.
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