2024-09-30 10:54:21 +02:00

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obj	wiki	repo	website	rev
application	https://en.wikipedia.org/wiki/PostGIS	https://git.osgeo.org/gitea/postgis/postgis	https://postgis.net	2024-09-30

PostGIS

PostGIS is a spatial database extender for PostgreSQL. It adds support for geographic objects allowing it to be used as a spatial database for geographic information systems (GIS). With PostGIS, PostgreSQL becomes a powerful database for managing spatial data and performing complex geographic operations.

PostGIS offers the following key features:

Geometry and Geography Types: PostGIS supports two primary types of spatial objects: Geometry (for Cartesian coordinates) and Geography (for geodetic coordinates).
Spatial Indexing: Support for R-tree-based spatial indexing using GiST (Generalized Search Tree) indexes.
Spatial Relationships and Measurements: Functions to perform spatial analysis, including distance calculations, intersections, unions, and more.
3D and 4D Coordinates: Support for 3D geometries (with Z values) and 4D (with M values for measures).
Raster and Vector Data: PostGIS allows for the handling of both raster (pixel-based) and vector (coordinate-based) spatial data.
WKT, WKB, GeoJSON Support: PostGIS supports common geographic data formats like Well-Known Text (WKT), Well-Known Binary (WKB), and GeoJSON.

Enable PostGIS in a PostgreSQL Database

After installation, to enable PostGIS on a specific database, run the following SQL commands:

CREATE EXTENSION postgis;
CREATE EXTENSION postgis_topology;

Spatial Data Types

PostGIS introduces several spatial data types. The two most commonly used types are:

1. `Geometry`

Represents geometric shapes in a Cartesian (planar) coordinate system.

CREATE TABLE my_table (
    id SERIAL PRIMARY KEY,
    geom GEOMETRY(Point, 4326)
);

2. `Geography`

Represents geographic shapes in a spherical coordinate system (uses latitudes and longitudes).

CREATE TABLE my_geo_table (
    id SERIAL PRIMARY KEY,
    geom GEOGRAPHY(POINT, 4326)
);

PostGIS also supports other geometry types, such as:

POINT
LINESTRING
POLYGON
MULTIPOINT
MULTILINESTRING
MULTIPOLYGON

Each of these types can be used in both GEOMETRY and GEOGRAPHY contexts.

Spatial Functions

PostGIS provides a vast library of spatial functions for querying and manipulating spatial data. Some important functions include:

Distance

Calculates the distance between two geometries.

SELECT ST_Distance(
    ST_GeomFromText('POINT(0 0)', 4326),
    ST_GeomFromText('POINT(1 1)', 4326)
);

Intersection

Returns the intersection of two geometries.

SELECT ST_Intersection(
    ST_GeomFromText('LINESTRING(0 0, 2 2)', 4326),
    ST_GeomFromText('LINESTRING(0 2, 2 0)', 4326)
);

Contains

Checks if one geometry contains another.

SELECT ST_Contains(
    ST_GeomFromText('POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))', 4326),
    ST_GeomFromText('POINT(1 1)', 4326)
);

Area

Calculates the area of a polygon.

SELECT ST_Area(
    ST_GeomFromText('POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))', 4326)
);

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