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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 encodes a spatially indexed (tiled) organization of primitive <Feature Topology> objects.
An <Aggregate Feature> can have more than one spatial organization for its topology. This allows various 'levels' or organizations. Perhaps at the 'top' <Aggregate Feature> under an <Environment Root>, one might find a single 10 km by 10 km spatial organization of topology spanning the entire transmittal, as well as one 500m by 500m 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 10km squares and one for the 500m 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 Features> or <Feature Model Instances>. 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> instances. When a single set of <Feature> instances is organized by multiple classification approaches, it's still the same set of <Features> being dealt with, and still the same set of <Feature Node>, <Feature Edge>, and <Feature Face> instances. Changing the logical organization of the <Feature> 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> instances, where the <Feature> instances are composed of the same spatially organized topological primitives, regardless of the organization from which the <Feature> instances are viewed.
| SE_Feature_Topology_Level | feature_topology_level; |
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| SE_Boolean | sparse; | |
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| SE_Integer_Positive | column_count; | |
| SE_Integer_Positive | row_count; | |
| SE_Long_Float | column_width; | (notes) |
| SE_Long_Float | row_width; | (notes) |
| SE_Spatial_Index_Spacing_Unit | spacing_unit; |
This is the origin of the collection, which is the lower-left corner.
This is the length of a cell in the given unit along the X axis.
This is the length of a cell in the given unit along the Y axis.
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