Getting Down To Earth: Geospatial Analysis With Rails

Presentation by Daniel Azuma from RailsConf 2012. Covers example implementations of geospatial projects in Ruby on Rails. For more info, see http://daniel-azuma.com/railsconf2012

Transcript

1. Getting Down to Earth: Daniel Azuma RailsConf 2012 Geospatial Analysis with Rails
2. Getting Down to Earth: Daniel Azuma RailsConf 2012 Geospatial Analysis with Rails
4. Daniel Azuma Rails Developer since 2006 Author of RGeo and related gems Chief Architect at Pirq
5. We’re hiring!
6. Beyond placing pushpins on a Google Map
7. Let’s dive directly into code We can worry about the concepts another time
8. Our agenda Setting up a geospatial Rails app Project 1: Visualizing geo-activity Project 2: Timezone lookup for a location Further material available online
9. Setting up Rails
10. Geospatial software stack libgeos — geometric algorithms libproj — coordinate projections PostGIS — spatial plugin for PostgreSQL RGeo — Ruby libraries
11. …use Postgres — it’s awesome…
13. …check out the README for more info…
15. We installed some software We created a Rails app as usual But there were a few more configs …and that’s it!
16. Project 1: Visualizing location activity
17. …use the “point” data type…
18. …configuring the migration…
19. …SRID 3785 is the Google Maps Mercator projection…
20. …make sure the index is marked “spatial”…
21. …configuring the model…
22. …assign an RGeo Factory to the model…
23. Need Input!
24. …some data to load…
26. …remember to transform coordinate systems…
27. Goal: visualize data on a map
28. …query for points in a rectangle…
29. …queries need to use the data’s coordinate system…
30. …search for overlap with the box…
31. Rectangles are not rectangular in geographic coordinates
33. …use Squeel — it’s awesome…
35. OUCH!
37. …create a heatmap in javascript…
39. Project 1 summary We created a model to hold location data We loaded a bunch of data into it We queried data within a map rectangle We visualized the data using a heatmap
40. Project 2: Location time zone lookup
41. World time zone regions
42. …a timezone has_many polygon regions…
44. …configure the migration…
45. …configure the model with an RGeo Factory…
46. http:/ /efele.net/maps/tz/world/
47. “I don’t even see the code anymore. All I see is point, polygon, circle…”
48. …load a shapefile as a stream of records…
49. …obtain the timezone object…
50. …populate the polygon table…
51. …query using the st_contains() SQL function…
55. …our original query…
56. …also query for “nearby” polygons…
57. …check the distance…
58. …distances also have a coordinate system…
59. …take the closest polygon…
60. Ain’t my fault you asked for st_distance…
63. …PostGIS can optimize intersections…
64. A “tall” table with many rows
65. A database index eliminates lots of rows quickly
66. Spatial databases are sometimes “fat”.
67. Reduce width by increasing the row count
68. Reduce width by increasing the row count
69. 4-to-1 subdivision
70. Looking for the sweet spot
72. …let’s add polygon subdivision…
75. …the core of the algorithm…
76. …check the number of sides…
77. …create a bounding box and subdivide…
78. …use RGeo — it’s awesome…
79. Whew! That was a lot of code!
80. Project 2 summary We created timezone and polygon models We loaded data from a shapefile We wrote queries for polygons containing a point, and intersecting a buffer. We further optimized queries by subdividing polygons
81. For further reading... http:/ /daniel-azuma.com/railsconf2012 …and look for the GeoRails Summit BOF