«Пространственные данные в Rails-приложениях» Сергей Нартымов (Минск), Sortware engineer at Brainspec, Rails, Rubinius, Elixir contributor

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