We write the name of a line passing through two different points A and B as “line AB” or as, the two-headed arrow over AB signifying a line passing through points A and B.Įxample: The following is a diagram of two lines: line AB and line HG. We may think of a line as a “straight” line that we might draw with a ruler on a piece of paper, except that in geometry, a line extends forever in both directions. measurement (How big is it?, How far is it?, …)īelow is the complete resource on Geometry originally created by The Math League.Ī line is one of the basic terms in geometry. art/patterns (designs, symmetries, representations, …).ĥ. navigating/star-gazing (How do I get from here to there?, using maps, …)Ĥ. machines/motion (using a pry-bar, riding a bike, sawing a board, swinging, …)ģ. building/structures (building/repairing a house, laying out a garden, making a kite, …)Ģ. It occurred in all cultures, through at least one of these five strands of human activities:ġ. The visual study of shapes, sizes, patterns, and positions. Input must be a point.As comprehensively defined by Cornell University’s Math department, Geometry is: 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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