H2GIS

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ST_Node

Signature

MULTILINESTRING ST_Node(GEOMETRY geom);

Description

Add nodes on a geometry for each intersections.

The resulting geometry is a MultiLinestring.

This function supports 3d coordinates and preserve z values only for input nodes. New calculated nodes have no z value.

Examples

With 2D Linestring

-- Initialize the input 2D Linestring layer
CREATE TABLE line AS SELECT 
  ST_GeomFromText('LINESTRING(1 1, 4 4, 1 4, 4 1)') as the_geom;
-- Compute nodes
CREATE TABLE nodes AS SELECT ST_NODE(the_geom) FROM line;

-- Answer: MULTILINESTRING ((1 1, 2.5 2.5), 
			    (2.5 2.5, 4 4, 1 4, 2.5 2.5), 
			    (2.5 2.5, 4 1))

With 3D Linestring

-- Initialize the input 3D Linestring layer
CREATE TABLE line AS SELECT 
  ST_GeomFromText('LINESTRING(1 1 0, 4 4 3, 1 4 3, 4 1 0)') as the_geom;
-- Compute nodes
CREATE TABLE nodes AS SELECT ST_NODE(the_geom) FROM line;

-- Answer: MULTILINESTRING ((1 1 0, 2.5 2.5), 
			    (2.5 2.5, 4 4 3, 1 4 3, 2.5 2.5), 
			    (2.5 2.5, 4 1 0))

With MultiLinestring

-- Initialize the input MultiLinestring layer
CREATE TABLE lines AS SELECT 
  ST_GeomFromText('MULTILINESTRING((1 1, 4 4), (1 3, 4 2))') as the_geom;
-- Compute nodes
CREATE TABLE nodes AS SELECT ST_NODE(the_geom) FROM lines;

-- Answer: MULTILINESTRING ((1 1, 2.5 2.5), (2.5 2.5, 4 4), 
			    (1 3, 2.5 2.5), (2.5 2.5, 4 2))

With MultiPolygon

-- Initialize the input MultiPolygon layer
CREATE TABLE polygon AS SELECT 
  ST_GeomFromText('MULTIPOLYGON(((1 1, 1 3, 3 3, 3 1, 1 1)), 
				((2 4, 4 4, 4 2, 2 2, 2 4)))') as the_geom;
-- Compute nodes
CREATE TABLE nodes AS SELECT ST_NODE(the_geom) FROM polygon;

-- Answer: MULTILINESTRING ((1 1, 1 3, 2 3), (2 3, 3 3, 3 2), 
			    (3 2, 3 1, 1 1), (2 4, 4 4, 4 2, 3 2), 
			    (3 2, 2 2, 2 3), (2 3, 2 4))

With GeometryCollection

-- Initialize the input GeometryColletion layer
CREATE TABLE geomColl AS SELECT 
  ST_GeomFromText('GEOMETRYCOLLECTION(
		      POLYGON ((1 1, 1 3, 3 3, 3 1, 1 1)), 
		      LINESTRING (1 4, 4 1))') as the_geom;
-- Compute nodes
CREATE TABLE nodes AS SELECT ST_NODE(the_geom) FROM geomColl;

-- Answer: MULTILINESTRING ((1 1, 1 3, 2 3), (2 3, 3 3, 3 2), 
			    (3 2, 3 1, 1 1), (1 4, 2 3), 
			    (2 3, 3 2), (3 2, 4 1))

See also