Discover PostGIS: Add Spatial functions to PostgreSQL

© 2018 EnterpriseDB® Corporation. All rights reserved. 1
DISCOVER POSTGIS
1
Mansur Shaikh
CONFIDENTIAL © Copyright EnterpriseDB Corporation, 2019. All rights reserved.

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Getting started with PostGIS

About PostGIS
• Refractions Research released first version in 2001 under
the GNU license
• Follows the Simple Features for SQL specification from the
Open Geospatial Consortium (OGC)
• Over 300 spatial operators and spatial functions
− Processing and analytical functions
• Spatial data types
• Spatial indexing
• Spatial reprojection
• Import / Export shapefiles (command line and GUI)
• Commands for importing raster data
• SQL commands to render and import data from multiple
formats such GeoJSON, KML, GML, and WTK
9

PostGIS : Getting started with spatial databases
• QGIS
− Open Source desktop GIS
• Enterprise GIS
− An integrated GIS system that is accessible throughout your organization
• Spatial database
− A centralized location for storing spatial data
− Spatial features for dealing with spatial data and analysis
• PostGIS
− A specific implementation of a spatial database built on the PostgreSQl database

PostGIS Data Types
Geometry
Geography
Raster Topology

PostGIS Data subtypes
Point
Linestring
Polygon
Multipoint
Multilinestring
Multipolygon

Spatial Definitions Examples (1 of 5)
Boundary

Equals

Getting started (loading data…)
17
INSERT into events_geo(eventname,geom,date)
SELECT eventname,
st_setsrid(st_makepoint(lon,lat),4326) as geom,date
FROM events;
Events Table
eventname character varying
lat double precision
lon double precision
Date timestamp with time zone
events_geo Table
eventname character varying
lat double precision
Lon double precision
Date timestamp with time zone

Getting started (visual inspection)
18

Getting started (visual inspection)
19

Getting started (Geometry Input and Output)
20
Example Input function
Insert into cities (name,state,geom)
Values (‘Bedford’,’MA’,
ST_GeomFromText(‘POINT(-71.248063 42.510547)’,4326));

Getting started (Power of GIS & SQL)
Create a route from a collection of waypoints captured in sequence
Write a function to tell whether a given lat/lon pair is
within a Point-Radius ring

34, 9
70, 12
Simple distance query between two points
SELECT ST_Distance
(ST_GeomFromText('POINT(34 9)’,4629),
ST_GeomFromText('POINT(70 12)’,4629));

Create a route from a collection of waypoints captured in sequence
Write a function to tell whether a given lat/lon pair is
within a Point-Radius ring

All the powerful tools of the RDBMS are available to you

Answer powerful questions with a simple query
Example Input function

What exactly is a spatial database ?
• Simple features standard (SFS) developed by Open Geospatial
Consortium
− Storage
− Geometry-BLOB Field
− Spatial functions (buffer, intersect, etc)
− PostGIS- ST_buffer(geom,400)
− SQL Server-geom.STBuffer(400)
− SQL/MM Spatial-extends SFS
• Spatial Indexes

Simple SQL Statement
• Select nest_id, recentstat, ST_Distance(geom, home) from raptor_nests
• Where recentspec=‘RTHA’
• Order by recentstat, nest_id;
• Why use SQl – Standard, Text based, store in database, backups in plain
text format, sent from web pages

© 2015 EnterpriseDB Corporation. All rights reserved. 29
PostGIS Installation

Installing PostGIS on your Local Computer
https://www.enterprisedb.com/downloads/postgis

PgAdmin4
Open PgAdmin4
Select on server and create server
Right click on database and create database -> sdb_course
Select sdb_course-> verify extensions and schemas and functions
Add PostGIS extension
Select sdb_course
Open query tool-> create extension postgis;
Verify functions, extensions and public schema
spatial_ref_sys

Installing QGIS : DEMO
• Download link
https://qgis.org/en/site/forusers/download.html

Loading Spatial data into PostGIS
− Resource file :- sdb_data.zip
− Loading shapefile
− Using PostGIS shapefile and dbf exporter
− Command line :- c:programefilespostgresql11bin
− raster2pgsql , shp2pgsql
− Open Postgres shapefile import/export manager
− View connection detail-> import->add file
− Goto S DB_DATA folder -> load baea-nests.shp and bowl_habitat.shp
− Give special reference id is 4326

Loading Spatial data into PostGIS using QGIS
• Load into QGIS and then put into PostGIS
− Any type of vector data you can load and view – ESRIGeo, or Jeojson, GPS file
− Select SDB_DATA folder from browser panel and drag and paste layers panel
− Select three file GBH_Rookeries.shp, Linear_Projects.shp, Raptor_Nests-shp
− First make connection
− Select database-> Dbmanager ->
− Make a connection with postgis from Browser panel -> provide connection information
− Click on basic for authentication and click on store -> Test connection
− List tables with no geometry
− Click on ok
− Click on import
− Give input file GBH_Rookeries, Linear_projects, Raptor_nests one by one
Go to PGAdmin4 and verify sdb_course with these five tables

Accessing PostGIS from the commandline, the pgAdmin, QGIS
− C:programefilepostgresql11binshp2pgsql
− C:programefilepostgresql11binraster2pgsql
− pgAdmin4
− Open query tools
 Select * from baue_nests
Some other tables with geometry column

4. Making SQL Spatial
• The PostGIS Vector Geometry model
• The Spatial reference ID
• The Geometry field
• Geometry vs Geography data type
• Spatial queries-working with Geometries
• Spatial queries-Measurement
• Spatial queries – Accessing the geometry

4. Vector Geometry Model
• Conforms to the OGC SFS standard
• Basic data structure is a Point
− 2 dimension –X and Y values. (longitude and latitude), projection
− 3 Dimension value- z values
• Line String is an array of points
• Polygon is an array of closed LineString’s
− First Linestring is an exterior ring
− Each following LineString is an interior ring

4. Vector Geometry Model. Cont..
• Multi-Part geometries
− Array of individual geometries
− Multipoint
− MultiLinestring
− MultiPolygon
• Features
− Geometry
− Attributes(field, properties,etc)

Spatial Reference ID
• Unique identifier for a coordinate reference system
− Coordinate System :- based in angles based on earth
− Projection
− Zone
− Datum
• In PostGIS you indicate the Spatial Reference by a number
• That number corresponds to well known Text
• Individual Geometries can have a spatial reference
• Geometry columns have a spatial reference

The Geometry field
• The geometry field is what makes a table spatial
• Its just a column in the database that can store a feature geometry
• It includes the SRID, the geometry type, and the actual coordinates in
binary form
• We can’t interpret the binary data but PostGIS provides a number of
functions that can output the geometry in human readable format
binary data could be picture, shape any things
These are functions that can output geometry as human redable text
• ST_AsText(), ST_AsEWKT(), ST_AsGeoJSON, etc.
• The combination of a geometry and the attribute that describes that
geometry is known as features

Geometry vs Geography
• Two different ways to store a features spatial information
− Geometry (data type). Based on plain surface
− Geography. (data type). Based on circular earth , math behind calculation is
complicated
• Geometry
− Based on planner surface
− Can be in a variety of coordinates reference systems defined by OGC
− Are mathematically simple
− Rich set of functions available
− OGC standard , GEOS libraries, etc.
− Accuracy declines as spatial extent increases.

Geometry vs Geography cont ..
• Geography
− Based on round earth
− Can only be in geographic coordinates system (latitude/longitude)
− Are mathematically complex
− Only support a fraction of the functions that are available for geometries
− Accurate measurements
− Which should you use ??
− Scale of your data and if larger distance use geography
− Availability of functions that you need
− performance

Working with Geometries
• What can we do with Geometries in PostGIS
− Get information about it
− GeometryType(geom) what type point, line or polygon
− ST_CoordDIM(geom). How many coordinate associate with each points
− ST_Dimension(geom). Like if line then it is one dimenstional, polygon is area which is two
dimensional
− ST_SRID(geom). :- special reference id for geometry
− ST_IsCollection(geom) :- returns true if geometry is single point or multipoint polygon
− ST_NumGeometries(geom),ST_NuminteriorRings(geom),ST_NumPoints(geom)
− ST_IsSimple(geom),ST_IsEmpty(geom),ST_IsClosed(geom),ST_isRing(geom)
− ST_IsValid(geom), ST_IsValidReason(geom)
• Change it’s spatial reference
• ST_SetSRID(geom,SRID) changes special reference id associated with that geometry
• ST_Transform(geom,SRID) converts one coordinate reference system to another

Spatial Queries :- Measurements
• What we can do with geometry ?
− Measure it
− ST_Length(line)
− Geometry- Cartesian length in SRID units
− Geography-length in meters over the spheroid
− ST_3DLength(line)
- Geometry-3D cartesian length using SRID
- Geography - Not supported
− ST_LengthSpheroid(line, spheroid)
− ST_Area(polygon)
− Geometry- cartesian area in SRID units
− Geography-area in square meters over the spheroid
− ST_Perimeter(polygon), ST_3DPerimeter(polygon)

Spatial Queries :- Accessing the Geometries
− Calculate distance from other geometries
− ST_Distance(geom1,geom2)
Geometry-cartesian distance in SRID units
Geography – length in meters over the spheroid
− ST_3DDistance(geom1,geom2)
- Geometry- cartesian distance using SRID in units
- Geography - Not supported
ST_DistanceSphere(geom1,geom2)
Geometry-cartesian area in SRID units squre degrees
Geography:- area in squre meters over the spheroid
ST_Perimeter(polygon), ST3DPerimeter(polygon)

Spatial Queries :- Accessing the Geometries
− Calculate distance from other geometries
− See it’s coordinate in text form
− ST_AsText(geom), ST_AsWKT(geom)
− ST_AsGeoJSON(geom)
− ST_AsGML(geom), ST_AsKML(geom)
− ST_AsMVT(table)
− Access it’s Coordinates
- ST_X(point), ST_Y(point), ST_Z(point), ST_M(point)
- ST_StartPoint(geom0, ST_EndPoint(geom)
− ST_PointN(geom,n), ST_LineinterpolatePoint(geom,proportion)
− ST_GeometryN(geom,n)
− ST_ExteriorRing(geom), ST_interiorRingN(geom,n)

• Docs - http://www.postgis.org/docs/
• PostGIS in Action, 2nd Edition
− http://www.amazon.com/gp/search?index=books&linkCode=qs&keywords=9781617291395
Resources:

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