PostGIS on Rails
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This document discusses using PostGIS to build location-aware applications. PostGIS extends PostgreSQL with spatial datatypes and functions to store and query geographic data. It allows querying data based on proximity and spatial relationships. The speaker provides examples of storing bear location data with PostGIS and querying to find bears within park boundaries or the number of bears in multiple parks. PostGIS enables building scalable location-aware applications and APIs.
![Bears (database
migration)
create_table :bears do |t|
t.column :lat, :float
t.column :lon, :float
end
add_index :bears, :lat
add_index :bears, :lon
add_index :bears, [:lat, :lon]
Friday, April 19, 13](https://image.slidesharecdn.com/postgisonrailslong-130419131246-phpapp02/85/PostGIS-on-Rails-13-320.jpg)
![A PostGIS example
(model)
def self.box(sw_lon, sw_lat, ne_lon, ne_lat)
factory = Rails.application.spatial_factory
sw = factory.point(sw_lon, sw_lat)
nw = factory.point(sw_lon, ne_lat)
ne = factory.point(ne_lon, ne_lat)
se = factory.point(ne_lon, sw_lat)
ring = factory.linear_ring([sw, nw, ne, se])
bbox = factory.polygon(ring)
self
.where('ST_Intersects(coordinates, :bbox)',
:bbox => bbox)
end
Friday, April 19, 16](https://image.slidesharecdn.com/postgisonrailslong-130419131246-phpapp02/85/PostGIS-on-Rails-16-320.jpg)
PostGIS on Rails
- 1. PostGIS on Rails Matt Nemenman matt@apartmentlist.com @quarterdome Friday, April 19, 1
- 2. About me Programmer Love maps Building map based rental search engine @ Apartment List Friday, April 19, 2
- 3. Location Aware Apps Where am I? What is around me? Friday, April 19, 3
- 4. Where am I? Latitude and Longitude HTML5 geolocation or GPS Address Geocoding Reverse geocoding Friday, April 19, 4
- 5. Where am I? What if you need to know ... Neighborhood School district National park Earthquake safety zone Friday, April 19, 5
- 6. What is around me? Yelp and Google Places API Restaurants, bars, etc. Points of interest Friday, April 19, 6
- 7. What is around me? What if you want to know ... What are three neighborhoods closest to me? Average rent for 1 bedroom in Lower Pacific Heights Crime rate on my city block Who is around me? Friday, April 19, 7
- 8. When 3rd party APIs fall short ... Get your own data set Build your own solution Friday, April 19, 8
- 9. Spatial Systems MongoDB Solr MySQL Oracle / DB2 PostGIS Friday, April 19, 9
- 10. PostGIS Geospatial extension to Postgres New datatypes Functions to work with those datatypes Spatial indices using GiST create extension postgis; Friday, April 19, 10
- 11. A Simple Example Friday, April 19, 11
- 12. A simple example Yosemite Park Ranger Tracking bears equipped with GPS transmitters Want to show all the bears on Google Maps Friday, April 19, 12
- 13. Bears (database migration) create_table :bears do |t| t.column :lat, :float t.column :lon, :float end add_index :bears, :lat add_index :bears, :lon add_index :bears, [:lat, :lon] Friday, April 19, 13
- 14. Bears (model) class Bear < ActiveRecord::Base def self.bbox(sw_lon, sw_lat, ne_lon, ne_lat) self .where( :lon => sw_lon..ne_lon ) .where( :lat => sw_lat..ne_lat ) end end Friday, April 19, 14
- 15. A PostGIS example (migration) create_table :bears do |t| t.column :coordinates, :geometry, :srid => 4326 end add_index :bears, :coordinates, :spatial => true Friday, April 19, 15
- 16. A PostGIS example (model) def self.box(sw_lon, sw_lat, ne_lon, ne_lat) factory = Rails.application.spatial_factory sw = factory.point(sw_lon, sw_lat) nw = factory.point(sw_lon, ne_lat) ne = factory.point(ne_lon, ne_lat) se = factory.point(ne_lon, sw_lat) ring = factory.linear_ring([sw, nw, ne, se]) bbox = factory.polygon(ring) self .where('ST_Intersects(coordinates, :bbox)', :bbox => bbox) end Friday, April 19, 16
- 17. A PostGIS example 1_000_000.times do Bear.create!( ...) end Friday, April 19, 17
- 18. 1,000,000 bears PostGIS is 1.5x to 50x faster Friday, April 19, 18
- 19. Active Record PostGIS Adapter Migration support Automatic conversion of PostGIS datatypes to Ruby (RGeo) objects and back gem 'pg' gem 'rgeo' gem 'activerecord-postgis-adapter' Friday, April 19, 19
- 20. Rails Migrations add_column :bears, :coordinates, :geometry, :srid => 4326 add_index :bears, :coordinates, :spatial => true Friday, April 19, 20
- 21. Postgres Table => d bears Table "public.bears" Column | Type -------------+----------------------------- id | integer coordinates | geometry(Geometry,4326) Indexes: "pins_pkey" PRIMARY KEY, btree (id) "index_pins_on_coordinates" gist (coordinates) Friday, April 19, 21
- 22. PostGIS Data => select id, coordinates from bears limit 4; id | coordinates ----+---------------------------------------------------- 1 | 0101000020E61000002A8A632C341F664021805D8DDBEB4BC0 2 | 0101000020E61000004DF900A54A5866C0A2BAB6AC827D50C0 3 | 0101000020E61000002450EA628F5259C01C789C77C2883040 4 | 0101000020E610000038760C7B85443C4013206005DC2C48C0 (4 rows) Friday, April 19, 22
- 23. RGeo ##> bear=Bear.first => #<Bear id: 1, coordinates: #<RGeo::Geos::CAPIPointImpl:0x3fd52ab501b4 "POINT (176.9751188224921 -55.84263770165877)">> ##> bear.coordinates.x => 176.9751188224921 ##> bear.coordinates.y => -55.84263770165877 Friday, April 19, 23
- 24. More examples # d parks Column | Type ------------------------+----------------------------- id | integer name | character varying(255) boundary | geometry(Geometry,4326) Indexes: "parks_pkey" PRIMARY KEY, btree (id) "index_parks_on_name" btree (name) "index_parks_on_boundary" gist (polygon) # select id, name, boundary from parks limit 2; id | name | boundary --------+-------------+------------------------ 1 | Yosemite |0103000020E6100000010000... 2 | Yellowstone |0103000020E6100000010000... Friday, April 19, 24
- 25. How many bears are in Yosemite now? ##> park = Park.find_by_name(Yosemite) ##> bears = Bear.where(ST_Intersects(coordinates, :bounds), :bounds => park.boundary) ##> bear_count = bears.count Friday, April 19, 25
- 26. How Many Bears in Yosemite and Yellowstone (Ruby)? ##> yosemite = Park.find_by_name(Yosemite) ##> yellowstone = Park.find_by_name(Yellowstone) ##> bounds = yosemite.boundary + yellowstone.boundary ##> bears = Bear.where(ST_Intersects(coordinates, :bounds), :bounds => bounds) ##> bear_count = bears.count Friday, April 19, 26
- 27. How Many Bears in Yosemite and Yellowstone (SQL)? select count(*) from bears inner join parks on ST_Intersects(bears.coordinates, parks.boundary) where parks.name in (Yosemite, Yellowstone); Friday, April 19, 27
- 28. Three parks closest to me? Distance operator (KNN) is a feature of Postgres 9.1 and above select id, name, boundary <-> ST_Point(37.775, -122.44) as distance from parks order by distance limit 3; Friday, April 19, 28
- 29. What else is possible? Friday, April 19, 29
- 30. Geometry Simplification ST_Simplify ST_ConvexHull ST_ConcaveHull Friday, April 19, 30
- 31. Spatial Relationships ST_Centroid ST_Contained ST_Area ST_Perimeter ST_DWithin Friday, April 19, 31
- 32. Format Conversions ST_AsGeoJSON ST_AsText Friday, April 19, 32
- 33. Do Try It at Home Heroku Postgres https://devcenter.heroku.com/articles/heroku- postgres-extensions-postgis-full-text-search Postgres.app http://postgresapp.com/ select postgis_full_version(); Friday, April 19, 33
- 34. Data Sources (free) US Census Data (Tiger) http://www.census.gov/geo/maps-data/data/tiger.html Zillow Neighborhoods http://www.zillow.com/howto/api/neighborhood- boundaries.htm Friday, April 19, 34
- 35. Data Sources (commercial) Maponics http://www.maponics.com/ Urban Mapping http://www.urbanmapping.com/ Onboard Informatics http://www.onboardinformatics.com/ Friday, April 19, 35
- 36. Links PostGIS http://postgis.net/ Active Record PostGIS Adapter https://github.com/dazuma/ activerecord-postgis-adapter RGeo https://github.com/dazuma/rgeo Friday, April 19, 36
- 37. Q & A We are hiring @apartmentlist! Friday, April 19, 37