TopoPolygon

A TopoPolygon is a topological Polygon item; it stores data about its relationship with other topological items.

TopoPolygons are spatially aware polygons that are aware of their spatial relationships with one another (for example, Administrative Districts whose boundaries can change) you should use Topological Polygons.

These items’ boundaries are made up of a series of connected Link items.

All data held by the TopoPolygon item is stored on its base Seed so TopoPolygon items are sometimes called Seed-Area items.

The seed point itself is often 'Blank' and not displayed.

If it is not blank, 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).

TopoPolygon Item

TopoPolygon creates TopoPolygon items from a Link and Node item structure.

  1. Select TopoPolygon.

  2. Within the Link and Node item network click inside a Polygon to turn it into a TopoPolygon item.

  3. If you do not wish to add further polygons to the TopoPolygon, proceed to step 4. In this case, the position you clicked becomes the seed point of the TopoPolygon.

    But to include more Polygons adjacent to the first, click within them one after another. Here SIS will decide where the seed point will be.

    The selected polygons which will form the TopoPolygon are shaded.

    To remove a selected polygon, simply click it again.

  1. Press Enter to complete the TopoPolygon.

  2. Repeat steps 2 to 4 to create more TopoPolygons if required.

SIS Desktop 9.1 will create the seed point at the first position you entered.

If you are having trouble forming the TopoPolygon item you want, check if Link items are crossing over each other without Node junctions.

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 are 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.

See also Item Properties