box_connectivity

syntax

box_connectivity(lower_bound(polygon_data_item), upper_bound(polygon_data_item))

definition

box_connectivity(lower_bound(polygon_data_item), upper_bound(polygon_data_item)) results in a new uint32 Domain unit with one entry for each ‘connection’ in the polygon_data_item Argument.

A ‘connection’ is a pair of bounding boxes that overlap or touch. The polygons themselves are not looked at, so a connection is a candidate pair, not a proof that the two polygons meet: Polygon_connectivity and the xxx_polygon_connectivity operators test the geometry, at a higher cost.

description

The function results in an F1 and F2 Attribute with relations to the Domain unit of the polygon_data_item attribute.

The relations indicate which connections exist, each connection only occurs once (a connection between polygon 0 and 1 only occurs as F1: 0 and F2: 1 and not vice versa).

This could be very useful to speed up partitioned unions, where the result of this operator can serve as the approximate partition.

see example

unit<uint32> SomePolygonSet 
{
	attribute<fpoint> geometry (poly);
	unit<uint32> BoxedConnectivity := box_connectivity(lower_bound(geometry), upper_bound(geometry));
	unit<uint32> ConnectParts      := connected_parts(BoxedConnectivity/F1, BoxedConnectivity/F2);
}
unit<uint32> SplitUnionedSet := bp_split_union_polygon(SomePolygonSet/geometry[rdc_cm], SomePolygonSet/ConnectParts/Part_rel);

conditions

The composition type type of the polygon_data_item Argument needs to be polygon with an ipoint, spoint, fpoint, or dpoint Value type.
The order of the points in polygon_data_item needs to be clockwise for exterior bounds and counter clockwise for holes in polygons (right-hand-rule).

since version

15.6.0

example

unit<uint32> connection := box_connectivity(lower_bound(district/geometry), upper_bound(district/geometry));