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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 (tiled) organization of primitive <Feature Topology> instances.
An <Aggregate Feature> instance can have more than one spatial organization for its topology. This allows various 'levels' or organizations. Perhaps at the 'top' <Aggregate Feature> instance under an <Environment Root> instance, one might find a single 10 kilometre by 10 kilometre spatial organization of topology spanning the entire transmittal, as well as one 500 metres by 500 metres spatial organization of topology also spanning the entire transmittal. That 'top' <Aggregate Feature> would have 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 SEDRIS, 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> 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's still the same set of <Feature Representation>s being dealt with, and still the same set of <Feature Node>, <Feature Edge>, 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.
| SE_Feature_Topology_Level | feature_topology_level; | (notes) |
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This is the origin of the collection, which is the lower-left corner.
The feature_topology_level field specifies the level of feature topology that is present within the hierarchy represented by the given <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 X axis.
The row_count field specifies the number of cells along the Y axis.
The column_width field specifies the length of a cell in the given unit along the X axis.
The row_width field specifies the length of a cell in the given unit along the Y axis.
The spacing_unit field specifies the unit of measurement used for the spacing of the spatial index.
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