Geospatial applications on Rails

1. Geospatial applications on Rails Sergey Nartimov Brainspec https://github.com/lest twitter: @just_lest
2. About • Rails, Rubinius, Elixir contributor • Software engineer at Brainspec Sergey Nartimov Brainspec https://github.com/lest twitter: @just_lest
3. Geospatial data
4. Geospatial data types • Point • Linestring • Polygon • Multi... • Geometry collection
5. Geospatial analysis • Coverage • Intersection • Distance • etc.
6. Geographic coordinate system
7. Geographic distance
8. Map projection
9. Mercator projection
11. Mercator projection
12. Mercator projection
13. Geospatial support
14. Geospatial support • MySQL • http://dev.mysql.com/doc/refman/5.5/en/ spatial-extensions.html
15. Geospatial support • MongoDB • http://www.mongodb.org/display/DOCS/ Geospatial+Indexing
16. Geospatial support • SpatiaLite • http://www.gaia-gis.it/gaia-sins/splite- doxy-4.0.0/index.html
17. Geospatial support • PostGIS • http://postgis.org/docs/
18. Rails & PostGIS
19. • https://github.com/dazuma/activerecord- postgis-adapter • https://github.com/dazuma/rgeo
20. # config/database.yml adapter: postgis # When postgresql >= 9.1 and postgis >= 2.0 postgis_extension: true # When postgresql < 9.1 or postgis < 2.0 # e.g. for postgresql 9.1 and postgis 1.5 on ubuntu script_dir: "/usr/share/postgresql/9.1/contrib/postgis-1.5" schema_search_path: public,postgis
21. create_table :locations do |t| t.point :coords, geographic: true end create_table :locations do |t| t.string :text t.point :coords, srid: 3785 end add_index :locations, :coords, spatial: true
22. class Location < ActiveRecord::Base GEOFACTORY = RGeo::Geographic.spherical_factory(srid: 4326) set_rgeo_factory_for_column :coords, GEOFACTORY end
23. Points in radius
24. point = Location::GEOFACTORY.point(27, 53) radius = 50_000 # 50 km Location.where('st_dwithin(coords, ?, ?)', point, radius) .order('st_distance(coords, ?)', point)
25. Squeel • https://github.com/ernie/squeel
26. point = Location::GEOFACTORY.point(27, 53) radius = 50_000 # 50 km Location.where { st_dwithin(coords, point, radius) } .order { st_distance(coords, point) }
27. class Location < ActiveRecord::Base GEOFACTORY = RGeo::Geographic.simple_mercator_factory set_rgeo_factory_for_column :coords, GEOFACTORY.projection_factory end point = Location::GEOFACTORY.point(27, 53) radius = 50_000 / Math.cos(lat * Math::PI / 180.0) Location.where { st_dwithin(coords, point, radius) } .order { st_distance(coords, point) }
28. Points in bounding box
31. sw = Location::GEOFACTORY.point(48.389537, 54.306922) ne = Location::GEOFACTORY.point(48.399643, 54.311216) bbox = RGeo::Cartesian::BoundingBox.create_from_points(sw, ne) Location.where('coords && ?', bbox)
32. Clustering • http://pgxn.org/dist/kmeans/ • http://postgis.refractions.net/docs/ ST_SnapToGrid.html
34. Time zones example
35. • http://efele.net/maps/tz/world/
37. • https://github.com/dazuma/rgeo-shapefile
38. class CreateTimeZonePolygons < ActiveRecord::Migration def change create_table :time_zone_polygons do |t| t.string :tzid t.geometry :geometry, geographic: true t.timestamps end add_index :time_zone_polygons, :geometry, spatial: true end end
39. class TimeZonePolygon < ActiveRecord::Base set_rgeo_factory_for_column :geometry, RGeo::Geographic.spherical_factory(srid: 4326) end
40. RGeo::Shapefile::Reader.open('tz_world.shp') do |file| file.each do |record| polygon = TimeZonePolygon.new polygon.tzid = record.attributes['TZID'] polygon.geometry = record.geometry polygon.save! end end
41. point = TimeZonePolygon::GEOFACTORY.point(27, 53) time_zone = TimeZonePolygon .where { st_covers(geometry, point) }.first time_zone.tzid # => "Europe/Minsk"
42. • Further improvements
43. Thanks <3 Sergey Nartimov Brainspec https://github.com/lest twitter: @just_lest