PostGIS Intro (一) -- geometries

• 空间数据库
  • 组成部分
  • geometry_columns 默认视图
  • 反映真实世界模型
    • Points
    • LineStrings
    • Polygons
    • Collections
  • Geometry 输入和输出格式
  • 出现的函数

空间数据库

组成部分

• Spatial Data Types
• Spatial Indexes and Bounding Boxes
• Spatial Functions

geometry_columns 默认视图

为数据库中的空间表信息，做一个基本的描述

• f_geometry_column 空间信息列名
• corrd_dimansion 几维图形 2-4
• srid
• type geom 的类型，Point、Polygon...

反映真实世界模型

• ST_GeometryType(geom)
• ST_NDims(geom)
• ST_SRID(geom)

Points

• ST_X(geometry)
• ST_Y(geometry)

LineStrings

• ST_Length(geometry) returns the length of the linestring
• ST_StartPoint(geometry) returns the first coordinate as a point
• ST_EndPoint(geometry) returns the last coordinate as a point
• ST_NPoints(geometry) returns the number of coordinates in the linestring

Polygons

Collections

• MultiPoint
• MultiLineString
• MultiPolygon
• GeometryCollection
  • st_numgeometries()

Geometry 输入和输出格式

出现的函数

• ST_Area: Returns the area of the surface if it is a polygon or multi-polygon. For “geometry” type area is in SRID units. For “geography” area is in square meters.

• ST_AsText: Returns the Well-Known Text (WKT) representation of the geometry/geography without SRID metadata.

• ST_AsBinary: Returns the Well-Known Binary (WKB) representation of the geometry/geography without SRID meta data.

• ST_EndPoint: Returns the last point of a LINESTRING geometry as a POINT.

• ST_AsEWKB: Returns the Well-Known Binary (WKB) representation of the geometry with SRID meta data.

• ST_AsEWKT: Returns the Well-Known Text (WKT) representation of the geometry with SRID meta data.

• ST_AsGeoJSON: Returns the geometry as a GeoJSON element.

• ST_AsGML: Returns the geometry as a GML version 2 or 3 element.

• ST_AsKML: Returns the geometry as a KML element. Several variants. Default version=2, default precision=15.

• ST_AsSVG: Returns a Geometry in SVG path data given a geometry or geography object.

• ST_ExteriorRing: Returns a line string representing the exterior ring of the POLYGON geometry. Return NULL if the geometry is not a polygon. Will not work with MULTIPOLYGON

• ST_GeometryN: Returns the 1-based Nth geometry if the geometry is a GEOMETRYCOLLECTION, MULTIPOINT, MULTILINESTRING, MULTICURVE or MULTIPOLYGON. Otherwise, return NULL.

• ST_GeomFromGML: Takes as input GML representation of geometry and outputs a PostGIS geometry object.

• ST_GeomFromKML: Takes as input KML representation of geometry and outputs a PostGIS geometry object

• ST_GeomFromText: Returns a specified ST_Geometry value from Well-Known Text representation (WKT).

• ST_GeomFromWKB: Creates a geometry instance from a Well-Known Binary geometry representation (WKB) and optional SRID.

• ST_GeometryType: Returns the geometry type of the ST_Geometry value.

• ST_InteriorRingN: 返回 polygon geometry 的内部边个数

• ST_Length: Returns the 2d length of the geometry if it is a linestring or multilinestring. geometry are in units of spatial reference and geography are in meters (default spheroid)

• ST_NDims: Returns coordinate dimension of the geometry as a small int. Values are: 2,3 or 4.

• ST_NPoints: Returns the number of points (vertexes) in a geometry.

• ST_NRings: If the geometry is a polygon or multi-polygon returns the number of rings.

• ST_NumGeometries: If geometry is a GEOMETRYCOLLECTION (or MULTI*) returns the number of geometries, otherwise return NULL.

• ST_Perimeter: 周长. (Polygon, Multipolygon)

• ST_SRID: Returns the spatial reference identifier for the ST_Geometry as defined in spatial_ref_sys table.

• ST_StartPoint: Returns the first point of a LINESTRING geometry as a POINT.

• ST_X: Returns the X coordinate of the point, or NULL if not available. Input must be a point.

• ST_Y: Returns the Y coordinate of the point, or NULL if not available. Input must be a point.