TopoPolygon

A TopoPolygon is a topological Polygon item that stores data regarding its topological relationship with other topological items, whose boundaries are made up of a series of connected Link items.

A TopoPolygon item is a Seed item upon which the definition of a topological polygon is stored. Since all of the data held by the TopoPolygon item is stored on its base Seed, TopoPolygon items are sometimes called Seed-Area items.

The seed point itself is often 'Blank' and not displayed. If it is not blank then it can be anywhere within the rectangular extents of the TopoPolygon. Commands that create TopoPolygon items try to position the seed point so that it lies inside the TopoPolygon itself (even when the TopoPolygon is horse-shoe shaped).

Properties

• Angle
• Area
• Clockwise
• Geometry class
• Links
• Number of loops
• Splinter factor
• Topology category
  

Item Properties

Properties

• Angle: _angleDeg#
  The angle of an item in degrees.
  
  
• Area: _area#
  The area covered by the item in square metres.
  
  
• Clockwise: _bClockwise&
  Is the item geometry defined in a clockwise direction?
  
  
• Geometry class: _classGeom$
  The C++ class used to store an item's geometry. This is handled automatically. You can see what precision an item's geometry is stored with by recognising the geometry classes.
  
  
• Links: _links$

A list of integers describing the Link items used by this Node, TopoPolygon or TopoLineString item.

Node:

A space-separated list of integers representing the Item IDs of links connected to this node.

A positive value indicates a link entering the node. A negative value indicates a link leaving the node.

e.g. -70 71 -79 80

TopoLineString:

A space-separated list of integers representing the Item IDs of links which constitute this TopoLineString.

The first integer is always 1. The second integer represents the number of links which constitute the TopoLineString. Subsequent integers represent the Item IDs of the links themselves. A negative integer means the direction along the link is opposite to the sense in which it is constructed.

e.g. 1 6 195 -183 161 -187 197 -189

TopoPolygon:

A space-separated list of integers representing the Item IDs of links which constitute this TopoPolygon.

The first integer is the number of loops in the TopoPolygon. The second integer represents the number of links in the first or only loop. This is followed by the Item IDs of the links which constitute the first or only loop. Any remaining integers represent further sets of “number of links/Item IDs”.  There are as many “number of links/Item IDs” sets as there are loops in the TopoPolygon. A negative integer means the direction of the TopoPolygon boundary along the link is opposite to the sense in which the link is constructed.

e.g. 3 3 238 -226 -224 4 235 218 -188 214 2 -194 -203

• Number of loops: _numloops&
  The number of loops used by a Polygon item. Most Polygon items have only one loop. However, any holes or islands will be stored as extra loops.
  
  
• Splinter factor: _splinter#
  The splinter factor of the Polygon. A circle has a splinter factor of 1. A very long and thin area could have a splinter factor of 100. Polygon items with large splinter factors are often produced by overlapping lines which are almost by not quite the same.
  
  
• Topology category: _cluster$
  The topological category for the TopoLineString or TopoPolygon item.
  
  Typical categories would be "Road" for TopoLineString items, and "House" for TopoPolygon items.
  

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