Partitioned_union_polygon (dissolve by attribute) - ObjectVision/GeoDMS GitHub Wiki

Geometric functions partitioned_union_polygon (dissolve by attribute)

• partitioned_union_polygon(polygon_data_item, relation)

partitioned_union_polygon(polygon_data_item, partioning) results in an attribute with all polygons from polygon_data_item, grouped by the argument relation.

Lines between adjacent polygons within each group are removed.

The domain unit of the resulting attribute is the values unit of the relation.

In other GIS software the term dissolve is often used for this operation.

• attribute polygon_data_item with an ipoint or spoint value type
• relation with a value type of the group CanBeDomainUnit

1. The composition type of the polygon_data_item item needs to be polygon.
2. The domain unit of the polygon_data_item item must be of value type uint32.
3. The domain unit of arguments polygon_data_item and relation must match.
4. The order of points in the polygon_data_item needs to be clockwise for exterior bounds and counter clockwise for holes in polygons (right-hand-rule).

This function result 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).

7.042

attribute<ipoint> geometry (polygon, region) := 
   partitioned_union_polygon(ipolygon(district/geometry), region_rel);

• union_polygon (dissolve)