Line geometry example1/27/2024 Input must be a point.This example shows how to create a line segment. ST_Y: Returns the Y coordinate of the point, or NULL if not available. ST_X: Returns the X coordinate of the point, or NULL if not available. ST_StartPoint: Returns the first point of a LINESTRING geometry as a POINT. ST_SRID: Returns the spatial reference identifier for the ST_Geometry as defined in spatial_ref_sys table. ST_Perimeter: Returns the length measurement of the boundary of an ST_Surface or ST_MultiSurface value. ST_NumGeometries: If geometry is a GEOMETRYCOLLECTION (or MULTI*) returns the number of geometries, otherwise return NULL. ST_NRings: If the geometry is a polygon or multi-polygon returns the number of rings. ST_NPoints: Returns the number of points (vertexes) in a geometry. ST_NDims: Returns coordinate dimension of the geometry as a small int. geometry are in units of spatial reference and geography are in meters (default spheroid) ST_Length: Returns the 2d length of the geometry if it is a linestring or multilinestring. Return NULL if the geometry is not a polygon or the given N is out of range. ST_InteriorRingN: Returns the Nth interior linestring ring of the polygon geometry. ST_GeometryType: Returns the geometry type of the ST_Geometry value. ST_GeomFromWKB: Creates a geometry instance from a Well-Known Binary geometry representation (WKB) and optional SRID. ST_GeomFromText: Returns a specified ST_Geometry value from Well-Known Text representation (WKT). ST_GeomFromKML: Takes as input KML representation of geometry and outputs a PostGIS geometry object ST_GeomFromGML: Takes as input GML representation of geometry and outputs a PostGIS geometry object. ST_GeometryN: Returns the 1-based Nth geometry if the geometry is a GEOMETRYCOLLECTION, MULTIPOINT, MULTILINESTRING, MULTICURVE or MULTIPOLYGON. Return NULL if the geometry is not a polygon. ST_ExteriorRing: Returns a line string representing the exterior ring of the POLYGON geometry. ST_AsSVG: Returns a Geometry in SVG path data given a geometry or geography object. ST_AsKML: Returns the geometry as a KML element. ST_AsGML: Returns the geometry as a GML version 2 or 3 element. ST_AsGeoJSON: Returns the geometry as a GeoJSON element. ST_AsEWKT: Returns the Well-Known Text (WKT) representation of the geometry with SRID meta data. ST_AsEWKB: Returns the Well-Known Binary (WKB) representation of the geometry with SRID meta data. ST_EndPoint: Returns the last point of a LINESTRING geometry as a POINT. ST_AsBinary: Returns the Well-Known Binary (WKB) representation of the geometry/geography without SRID meta data. ST_AsText: Returns the Well-Known Text (WKT) representation of the geometry/geography without SRID metadata. For “geography” area is in square meters. For “geometry” type area is in SRID units. ST_Area: Returns the area of the surface if it is a polygon or multi-polygon. The following SQL query shows an example of WKB representation (the call to encode() is required to convert the binary output into an ASCII form for printing): Note that in addition to a text parameter with a geometry representation, we also have a numeric parameter providing the SRID of the geometry. The most common use of a constructor is to turn a text representation of a geometry into an internal representation: ST_GeomFromText(text, srid) returns geometry Fortunately, PostGIS supports emitting and consuming geometries in a large number of formats: In order for external programs to insert and retrieve useful geometries, they need to be converted into a format that other applications can understand. Within the database, geometries are stored on disk in a format only used by the PostGIS program.
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