add postgis

technology/applications/development/PostGIS.md

@@ -0,0 +1,103 @@
+---
+obj: application
+wiki: https://en.wikipedia.org/wiki/PostGIS
+repo: https://git.osgeo.org/gitea/postgis/postgis
+website: https://postgis.net
+rev: 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:
+
+```sql
+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.
+
+```sql
+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).
+
+```sql
+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.
+
+```sql
+SELECT ST_Distance(
+    ST_GeomFromText('POINT(0 0)', 4326),
+    ST_GeomFromText('POINT(1 1)', 4326)
+);
+```
+
+### Intersection
+Returns the intersection of two geometries.
+
+```sql
+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.
+
+```sql
+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.
+
+```sql
+SELECT ST_Area(
+    ST_GeomFromText('POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))', 4326)
+);
+```