Split_polygon

geometric-functions split_polygon

syntax

  • split_polygon(polygon_data_item)

description

split_polygon(polygon_data_item) results in a new uint32 domain-unit with single polygons for each (multi)polygon in the polygon_data_item argument.

If the original polygon_data_item only contains single polygons, the resulting domain unit has the same number of elements as the domain unit of the polygon_data_item argument.

The figure illustrates a source polygon_data_item (left image) of a domain unit with four entries.

Each color represents an entry in the polygon_data_item, the red and green areas are multipolygons.

The resulting domain unit of the split_polygon function for this polygon_data_item will contain seven entries, with a single polygon for each entry (right image).

The split_polygon functions generates two (and since GeoDMS 8) 3 subitems:

  • geometry: the geometry of the single polygons. This attribute has the same values-unit as the polygon_data_item argument.
  • nr_OrgEntity: a relation for the new domain towards the domain of the polygon_data_item argument.
  • polygon_rel: a relation for the new domain towards the domain of the polygon_data_item argument. This data item is a copy of the nr_OrgEntity, but whith a name that meets our naming-conventions. The nr_OrgEntity argument is still generated for backward compatibility.

We advice to use the polygon_rel argument, the nr_OrgEntity argument will be phased out.

applies to

attribute polygon_data_item with an ipoint or spoint value-type

conditions

  1. The composition type of the polygon_data_item argument needs to be polygon.
  2. The domain unit of the polygon_data_item argument must be of value type uint32.

This function results in problems for (integer) coordinates larger than 2^25 (after translation where the first point is moved to (0, 0)). If your integer coordinates for instance represent mm, 2^25[mm] = about 33 [km]. The reason is that for calculating intersections, products of coordinates are calculated and casted to float64 with a 53 bits mantissa (in the development/test environment of boost::polygon these were float80 values with a 64 bits mantissa). We advise to keep the size of your integer coordinates for polygons limited and for instance do not use a mm precision for country borders (meter or kilometer might be sufficient).

since version

7.042

example 

unit<uint32> split_polygons := split_polygon(geometry);

The number or resulting entries is based on the number of null coordinates plus 1.

see also