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
   

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2. Getting Down to Earth:
   Daniel Azuma
   RailsConf 2012
   Geospatial Analysis
   with Rails
   

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4. Daniel Azuma
   Rails Developer
   since 2006
   Author of RGeo
   and related gems
   Chief Architect
   at Pirq
   

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5. We’re hiring!
   

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6. Beyond placing pushpins
   on a Google Map
   

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7. Let’s dive directly into code
   We can worry about the concepts another time
   

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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
   

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9. Setting up Rails
   

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10. Geospatial software stack
    libgeos — geometric algorithms
    libproj — coordinate projections
    PostGIS — spatial plugin for PostgreSQL
    RGeo — Ruby libraries
    

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11. …use Postgres — it’s awesome…
    

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13. …check out the README for more info…
    

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15. We installed some software
    We created a Rails app as usual
    But there were a few more configs
    …and that’s it!
    

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16. Project 1:
    Visualizing location activity
    

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17. …use the “point” data type…
    

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18. …configuring the migration…
    

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19. …SRID 3785 is the Google
    Maps Mercator projection…
    

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20. …make sure the index is marked “spatial”…
    

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21. …configuring the model…
    

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22. …assign an RGeo Factory to the model…
    

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23. Need Input!
    

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24. …some data to load…
    

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26. …remember to transform coordinate systems…
    

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27. Goal: visualize data on a map
    

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28. …query for points in a rectangle…
    

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29. …queries need to use the
    data’s coordinate system…
    

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30. …search for overlap with the box…
    

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31. Rectangles are not rectangular
    in geographic coordinates
    

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33. …use Squeel — it’s awesome…
    

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35. OUCH!
    

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37. …create a heatmap in javascript…
    

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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
    

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40. Project 2:
    Location time zone lookup
    

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41. World time zone regions
    

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42. …a timezone has_many polygon regions…
    

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44. …configure the migration…
    

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45. …configure the model with an RGeo Factory…
    

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46. http:/
    /efele.net/maps/tz/world/
    

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47. “I don’t even see the code anymore.
    All I see is point, polygon, circle…”
    

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48. …load a shapefile as a stream of records…
    

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49. …obtain the timezone object…
    

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50. …populate the polygon table…
    

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51. …query using the st_contains() SQL function…
    

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55. …our original query…
    

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56. …also query for “nearby” polygons…
    

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57. …check the distance…
    

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58. …distances also have a coordinate system…
    

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59. …take the closest polygon…
    

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60. Ain’t my fault
    you asked for
    st_distance…
    

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63. …PostGIS can optimize intersections…
    

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64. A “tall” table
    with many rows
    

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65. A database index
    eliminates lots of
    rows quickly
    

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66. Spatial databases are sometimes “fat”.
    

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67. Reduce width
    by increasing
    the row count
    

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68. Reduce width
    by increasing
    the row count
    

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69. 4-to-1 subdivision
    

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70. Looking for the sweet spot
    

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72. …let’s add polygon subdivision…
    

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75. …the core of the algorithm…
    

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76. …check the number of sides…
    

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77. …create a bounding box and subdivide…
    

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78. …use RGeo — it’s awesome…
    

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79. Whew! That was
    a lot of code!
    

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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
    

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81. For further reading...
    http:/
    /daniel-azuma.com/railsconf2012
    …and look for the GeoRails Summit BOF
    

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