Using PostGIS To Add Some Spatial Flavor To Your Application

Using PostGIS to add some spatial flavor to your applications Steven Citron-Pousty Developer Evangelist deCarta

Agenda

What is PostGIS

Installing

Getting data and importing

Using in an application

ASK QUESTIONS ALL ALONG

Assumptions about you

Know PostgreSQL and SQL

New to spatial analysis and PostGIS

Mainly using a commercial mapping service for your base layers

Interested in writing cool applications

This will only be a short shallow introduction

What is PostGIS

PostGIS adds support for geographic objects and geographic functions to PostgreSQL

Points, Lines, Polygon, and Linear References

Spatial function such as area, near, overlap, within, clip, and simplify

Competitive Offerings

MySQL – doesn’t really implement all the functions and it only deals with bounding boxes

SQLServer – only in SQLServer2008 but supported on all editions

Oracle Spatial – full featured and includes a broad range of client libraries

DB2 and Sybase and Informix and Ingres

ESRI’s SDE can use PostGIS as a DB

Installing

Other libraries you want

Proj4.5 for projection

GEOS 3.0 for spatial operations

Windows – use the “application stack builder”

There are RPMs on the PostGIS site – not always the latest

You can use Synaptic for Ubuntu – not always the latest

Build is really simple, as long as you have required libraries installed

Other Steps

Add the objects and functions from the provided SQL files

Best practice is to make these into a template for future databases

From there making DBs is easy cheesy

Two more things you need to understand Almost there – I promise

Shapefiles when is a file not a file

Projections and Datums

More Projection Goodness

EPSG (European Petroleum Survey Group) has a number for most projections and datum combinations

deCarta, and those other no names, expect geographic coordinates with WGS84 datum

EPSG:4326

Geographic coordinates system with WGS84 datum.

Degrees are not constant distance as you move North and South

Not very accurate for distance and area calcs except over small areas

You want to use projected layers (or project on the fly) for area and distance calcs

Projecting using ogr2ogr

Assuming there is a .prj file you need to find your output projection

http://Spatialreference.org

ogr2ogr -t_srs EPSG:4326 -f "ESRI Shapefile" water_bodies_gcs.shp water_bodies.shp

Now let’s make some SQL

Shp2pgsql is a command-line utility to take a shapefile to a SQL file

The geometry field is called the_geom

shp2pgsql.exe -s 4326 -I C:datawater_bodies_gcs.shp waterbodies > C:datawaterbodies.sql

Y’all know what to do with SQL

psql -q -U postgres -f C:datawaterbodies.sql kerncounty

With lots-o-features you want to use –q option to prevent spamming your terminal

Let’s get this party started

SELECT gid, the_geom FROM waterbodies WHERE gid = 2;

gid | the_geom

-----+------------------------------------------------------------------------------------------------------------------------ 2 |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

WTF!

Well Known Text (WKT)

SELECT gid, asText(the_geom) AS Geometry FROM waterbodies WHERE gid = 2;

gid | geometry

-----+------------------------------------------------------------------------------------------------------------------

2 | MULTIPOLYGON(((-119.100632086203 35.4055119715638,-119.100588218445 35.4055112058011,-119.100531231104 35.4054841485633,-119.100512429531 35.4054574696738,-119.100503538195 35.4054055329503,-119.100511130385 35.4053601605257,-119.100535206075 35.405321352397,-119.100553022028 35.405274210549,-119.100556605305 35.4052355857659,-119.100546090324 35.4052155445137,-119.100508823288 35.4051873528921,-119.100446853726 35.4051605904963,-119.100399340328 35.4051228925546,-119.100391835921 35.4050940667872,-119.100372950847 35.4050639704809,-119.100375365397 35.405015718586,-119.100425812278 35.4049565392201,-119.10050149939 35.4049457944043,-119.100564470279 35.4049714612528,-119.100604563231 35.4050078531802,-119.100599831265 35.4050489697935,-119.100584596379 35.4050945039903,-119.100567940388 35.4051324845866,-119.1005698232335.4051746229123,-119.10058625583 35.4052187928558,-119.100622330944 35.4052508971182,-119.100619921668 35.4052682131054,-19.100598089049 35.4052968351787,-119.100577998689 35.4053291714179,-119.100575017479 35.4053658960572,-119.100604549953 35.405402382471,-119.100637922046 35.4054192567285,-119.100664242372 35.4054234663778,-119.100695837816 35.4054166982392,-119.100720934285 35.4053849237043,-119.100753214358 35.4053632206036,-119.100782184037 35.405357556842,-119.100815518089 35.4053821192651,-119.100819868035 35.4054112646836,-119.10080955272 35.4054297323306,-119.100779407259 35.4054462156383,-119.100715985448 35.4054424595886,-119.100683185361 35.405457885726,-119.100686085296 35.4054773160076,-119.100676349209 35.4054947310111,-119.100632086203 35.4055119715638)))

Lesson Learned

Ask for your responses in Text format when you want to know what is going on

eWKT includes the projection information 'SRID=4326;MULTIPOLYGON(((-119.5 35.0, -119.0 35.0, -119.0 35.5, -119.5 35.5, -119.5 35.0)))'

asKML, asSVG, or asGML

SELECT asKML(the_geom) FROM watercourses WHERE gid = 17;

Inserting a new record

Projection has to match

INSERT INTO firestations(station_na, the_geom) VALUES('Best LittleFire House in CA', ST_SetSRID(ST_MakePoint(-119.5, 34.5), 4326) );

Select using the geometry

Distance

In units of the underlying coverage

SELECT gid FROM waterbodies WHERE ST_DWithin('SRID=4326;POINT (-119.103762382096 35.4122898449297)', the_geom, 0.005); gid ----- 4 5 6 7 8

Let’s find all the parcels in Agricultural Zones SELECT p.gid FROM parcels AS p, zoning AS z WHERE z.comb_zn LIKE 'A%' AND ST_Within(p.the_geom, z.the_geom);

Do something with the geometry after selection

Calculating Area SELECT sum(ST_Area(z.the_geom)) FROM zoning AS z WHERE z.comb_zn LIKE 'NR%'; sum -------------------- 0.0131834159551545

Turn polygons into points SELECT gid, asText(ST_Centroid(the_geom)) FROM waterbodies WHERE gid = 124; gid | geometry -----+------------------------------------------- 124 | POINT(-118.427120958287 35.6702299014044) SELECT gid, asText(ST_PointOnSurface(the_geom)) FROM waterbodies WHERE gid = 124; gid | geometry -----+------------------------------------------- 124 | POINT(-118.449967685908 35.6911672413056)

Create new tables using a select CREATE TABLE biglake WITH OIDS AS SELECT gid, the_geom FROM waterbodies WHERE gid = 124; SELECT ST_AREA(the_geom) FROM biglake; st_area --------------------- 0.00313986591299908

Buffering

Some SQL to buffer SELECT ST_Area(ST_Buffer(the_geom, 0.1)) FROM biglake; st_area -------------------- 0.0718529848413709 Remember that is used to be 0.003

Spatial Operators

Clip to the bounding box SELECT gid, ST_Intersection(the_geom, 'SRID=4326;MULTIPOLYGON((( -119.5 35.0, -119.0 35.0, -119.0 35.5, -119.5 35.5, -119.5 35.0)))') FROM watercourses WHERE ST_Intersects(the_geom, 'SRID=4326;MULTIPOLYGON((( -119.5 35.0, -119.0 35.0, -119.0 35.5, -119.5 35.5, -119.5 35.0)))');

Simplifying geometries

Most geometries have more information than you can display

There are algorithms for weeding out points

Trade-off retaining “shape” versus less points

Select ST_NPoints(the_geom) FROM watercourses WHERE gid IN (12, 14, 17); st_npoints ------------ 265 68 48

SELECT ST_NPoints(ST_Simplify(the_geom, 0.00001)) FROM watercourses WHERE gid IN (12, 14, 17); st_npoints ------------ 65 19 18

SELECT ST_NPoints(ST_Simplify(the_geom, 0.0001)) FROM watercourses WHERE gid IN (12, 14, 17); st_npoints ------------ 18 6 7

So how do you bring this together in an app

Never send 3000 pts to the browser

Putting your information in a DB gives you way more control over what you return and display

http://demo.decarta.com/opensearchservice/index.html

Where do you go now - PostGIS

Home

http://postgis.refractions.net/

Tools to use with PostGIS

http://postgis.refractions.net/support/wiki/index.php?ToolsSupportPostgis

Good support Wiki

http://postgis.refractions.net/support/wiki/

Another Introduction

http://www.mapbender.org/presentations/Spatial_Data_Management_Arnulf_Christl/Spatial_Data_Management_Arnulf_Christl.pdf

Great OS-GEO resources

http://www.bostongis.com/

PostGIS specific

http://www.bostongis.com/postgis_quickguide.bqg?outputformat=PDF

Nice GIS on a Stick for Windows http://www.archaeogeek.com/blog/portable-gis /

Where to get Data

Kern County

http://www.co.kern.ca.us/gis/downloads.asp

California

http://gis.ca.gov/casil/

US Census

http://www.census.gov/geo/www/tiger/

Some UN

http://www.grida.no/gis/index.htm

http://www.geographynetwork.com/

http://gos2.geodata.gov/wps/portal/gos

Open source Data

http://www.fortiusone.com/

OSM

http:// wiki.openstreetmap.org/index.php/Planet.osm

http://code.google.com/p/osm2shp/

Map API to use

http://developer.decarta.com

Free to develop – sign up and be mapping and mashing within 12 hours

If you want a web page with JavaScript look at the JavaScript API

If you want to use Web Services then look at the web services area on the left

Using PostGIS To Add Some Spatial Flavor To Your Application

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