Spatial concepts

Geometry types

For a more complete description of the geometry types, refer to the OpenGIS standard specification.

Geometric Properties

Simple and non-simple geometries

As defined in the OpenGIS standard, a simple geometry is one that does not have any “anomalous” geometric points, such as self intersection or self tangency. Each geometric type defines its simple and non-simple aspects. Some examples of non-simple geometries include: a polygon with vertices inside the area of the polygon itself; a linestring that intersects itself; a multipoint that has two points with equal coordinates; a polygon with an interior ring that touches the polygon’s boundary. See Figure 2: Simple and Non-Simple Geometries.

#spatial__fig_spatial_snons shows some examples of simple and non-simple geometries. The two geometries on the left are simple geometries that do not intersect within themselves. On the right side, both the linestring and the polygon have self-intersecting lines, and thus are non-simple. By default, the Netezza Performance Server Spatial cartridge supports only simple geometries; thus, a geometric object definition that is non-simple cannot be inserted or loaded. The only exception is when a geometry is created and the “skipSimpleTest” parameter is set to true (ST_WKBToSQL() and ST_WKTToSQL()).

#spatial__fig_sampsim shows a sample SQL query to add the linestring object illustrated in the Cartesian grid to a table named geomtable. The query successfully adds the linestring object.

#spatial__fig_sampnonsim shows a sample query that defines the non-simple linestring object illustrated in the grid.

Note that the 1st SQL query returns an error. The 2nd SQL query has the exact same non simple geometry but is successful since the skipSimpleTest is set to “true”.

Note that loading of non-simple geometric data can lead to unexpected, incorrect results when analyzing the non-simple geometries for values such as distance, area, contains, or intersections. To load geometric data from other sources to the Netezza Performance Server database, best practices are available for dealing with potential non-simple geometries in the data.

Spatial geometry types

ST_Point
ST_Curve (non-instantiable)
ST_Linestring
ST_Surface (non-instantiable)
ST_Polygon
ST_Multipoint
ST_MultiCurve (non-instantiable)
ST_MultiLineString
ST_MultiSurface (non-instantiable)
ST_MultiPolygon
ST_GeomCollection

ST_Polyhedral
ST_Text

In the OpenGIS standard, each geometry type has a defined integer value. #spatial__table_opengis shows the integer code values and the number of coordinates for each type. These codes are used by the Netezza Performance Server spatial functions.