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Location Location Location

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Location
                                  Location
                                  Location

                      Gavi...

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Friday, 12 April 13

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GPS, Location, GIS, and
                       Spatial Relationships
                      • GPS Technology
              ...

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Location Location Location

  1. 1. Location Location Location Gavin Heavyside - ACCU 2013 - 12 April 2012 gavin@heavyside.co.uk @gavinheavyside Friday, 12 April 13
  2. 2. Friday, 12 April 13
  3. 3. GPS, Location, GIS, and Spatial Relationships • GPS Technology • GIS and Mapping Concepts • Spatial DBs and SQL • Practical Example Friday, 12 April 13
  4. 4. Friday, 12 April 13
  5. 5. • www.mydrivesolutions.com • Insurance telematics • Linux,Ruby, Rails, Postgres, PostGIS, NoSQL, Chef, AWS, C++ Friday, 12 April 13
  6. 6. Friday, 12 April 13
  7. 7. • I have no idea what I’m doing Friday, 12 April 13
  8. 8. GPS • Currently 32 satellites Friday, 12 April 13
  9. 9. GPS Friday, 12 April 13
  10. 10. Basic GPS Concepts • 24+ Satellites orbit the earth • Atomic clocks • Each constantly transmits its time and location Friday, 12 April 13
  11. 11. Basic GPS Concepts • Normally 4 or more sats used by receiver • Distance to each satellite calculated using speed of light • Triangulate position • Derived attributes - speed, bearing Friday, 12 April 13
  12. 12. http://www.ausairpower.net/TE-GPS-Guided-Weps.html Friday, 12 April 13
  13. 13. Almanac and Ephemeris • Almanac: GPS constellation info, orbits • Ephemeris: orbital and clock correction • With both in memory, lock is faster • A-GPS gets ephemeris from internet Friday, 12 April 13
  14. 14. NMEA 0183 • Serial ASCII data format • CSV ‘sentences’ for different types of data Friday, 12 April 13
  15. 15. NMEA Sentences • GGA - Fix information • GSA - DOP and active satellites • GSV - Satellites in view • RMC - Time, date and position Friday, 12 April 13
  16. 16. Friday, 12 April 13
  17. 17. Problems with GPS • Noise • Urban Canyons • Multipath signals • Solar flares and atmospherics • Mounting of receiver Friday, 12 April 13
  18. 18. Others • GLONASS • BEIDOU/COMPASS • GALILEO • IRNSS Friday, 12 April 13
  19. 19. Smartphone Support • All major smartphones have GPS sensors • Balance accuracy, frequency, battery life • Usually subscribe to service and get called back with location updates • Alerts: Geofencing, Significant Change Friday, 12 April 13
  20. 20. HTML5 GeoLocation Friday, 12 April 13
  21. 21. Friday, 12 April 13
  22. 22. Digital Maps • Commercial • NAVTEQ, Tele Atlas • Free • OSM • Online • Google, Bing, etc Friday, 12 April 13
  23. 23. Display • Usually map tiles at different zoom levels • Server will return tiled images for a bounding box • Plenty of libraries commercial or free to embed in apps or web pages • Add your own overlay markers and layers Friday, 12 April 13
  24. 24. Leaflet • JS plugin • Uses OSM or other tile servers • HW accelerated, touch-compatible • Markers, Polygons, Layers, GeoJSON • http://leafletjs.com Friday, 12 April 13
  25. 25. Friday, 12 April 13
  26. 26. Digital maps for GIS • Vector representation of your map • Commercial or OSM • Use the road or feature geometry, in conjunction with attributes of the features Friday, 12 April 13
  27. 27. OpenStreetMap • http://www.openstreetmap.org/ • Community generated and curated • XML geometry and metadata composed of nodes, ways, and relations • Can be downloaded in regions, updated incrementally Friday, 12 April 13
  28. 28. Friday, 12 April 13
  29. 29. Friday, 12 April 13
  30. 30. • Some people when faced with a problem think “I know, I’ll use XML”. Now they have Friday, 12 April 13
  31. 31. Data Formats Friday, 12 April 13
  32. 32. Geometry Types • Points • Linestrings • Polygons • Compound: MultiPoint etc • 3D: all above with elevation, Polyhedrals Friday, 12 April 13
  33. 33. Well-Known Text (WKT) • markup language for vector geometry • ISO standard, originally by OGC • Always uses X Y, so watch out when using lat and lon: needs to be (lon lat) • Also an equivalent Well Known Binary used by databases to store spatial data • Can embed SRID (see later) Friday, 12 April 13
  34. 34. WKT Examples • Point(30 10) • LINESTRING (30 10, 10 30, 40 40) • POLYGON ((30 10, 10 20, 20 40, 40 40, 30 10)) • POLYGON ((35 10, 10 20, 15 40, 45 45, 35 10),(20 30, 35 35, 30 20, 20 30)) Friday, 12 April 13
  35. 35. KML • XML data format used by Google Earth • Supports points, lines, markers, polygons, overlays, and much much more • Zip up with assets (e.g. Collada 3D models) into a .kmz file Friday, 12 April 13
  36. 36. KML Friday, 12 April 13
  37. 37. Friday, 12 April 13
  38. 38. GeoJSON Friday, 12 April 13
  39. 39. ShapeFiles • Created by ESRI • Widely used and understood • Points, Lines, Polygons • Collection of files: .shp, .shx, .dbf, others • Can be imported straight into PostGIS with shp2pgsql Friday, 12 April 13
  40. 40. Friday, 12 April 13
  41. 41. Spatial Reference Systems • The Earth is not flat • Neither is it a spheroid • nor even an ellipsoid • Spatial Reference Systems approximate the geoid of the earth to an ellipsoid Friday, 12 April 13
  42. 42. Geoid Friday, 12 April 13
  43. 43. WGS84 • The most common (and most useful) spatial reference system • best fitting ellipsoid model to the reference points on the 1996 Earth Gravitational Model geoid • Used by GPS Friday, 12 April 13
  44. 44. Friday, 12 April 13
  45. 45. Projections • Projections • Orientation • Cylindrical • Oblique • Conic • Equatorial • Azimuthal • Transverse Friday, 12 April 13
  46. 46. Transverse Mercator • Some projections look good over most of the globe • Some are only useful locally (e.g. UTM) Friday, 12 April 13
  47. 47. Geospatial Databases • Ordinary RDBs with support for spatial data types • NoSQL DBs • MongoDB • https://github.com/neo4j/spatial Friday, 12 April 13
  48. 48. PostGIS • http://postgis.org/ • Geospatial Extensions for PostgreSQL • Excellent support for spatial data, operations, indexes • Actively developed Friday, 12 April 13
  49. 49. Creating a PostGIS DB Friday, 12 April 13
  50. 50. Spatial Relationships • Many ways to compare geometries • Some can compare different types • Some only valid for same type • CONTAINS, CROSSES, DISJOINT, DISTANCE, DWITHIN, EQUALS, INTERSECTS, OVERLAPS, TOUCHES, WITHIN Friday, 12 April 13
  51. 51. ST_Equals Friday, 12 April 13
  52. 52. ST_Intersects Friday, 12 April 13
  53. 53. ST_DWithin Friday, 12 April 13
  54. 54. ST_Transform Friday, 12 April 13
  55. 55. Geography Data Type • Usually measurements are in the units of the spatial reference system • Radians for SRID 4326 (WGS84) • The geography data type can help Friday, 12 April 13
  56. 56. Geospatial Indexes • Indexes on geo columns are necessary • Covers bounding boxes • Reduces search space • Geos used for calculations Friday, 12 April 13
  57. 57. EXPLAIN • Use EXPLAIN to check the planner is using spatial indexes, just like other SQL queries Friday, 12 April 13
  58. 58. Ordnance Survey OpenData • http://www.ordnancesurvey.co.uk/ oswebsite/products/os-opendata.html • Vector & Raster data • Maps, Roads, Boundaries, Postcodes Friday, 12 April 13
  59. 59. Friday, 12 April 13
  60. 60. Code-Point Open • CSV "Database" of UK postcode • (Not Northern Ireland) • 1.6m+ postcodes • Eastings and Northings for each entry • Also county/district & NHS info Friday, 12 April 13
  61. 61. Data Format • Postcode in field 1 Friday, 12 April 13
  62. 62. Data Format • Eastings, Northings in fields 3,4 Friday, 12 April 13
  63. 63. OS National Grid Friday, 12 April 13
  64. 64. Geocoding • Find the geographic location of a feature, e.g. address, business, POI • Reverse: Find a feature from a geographic location (e.g. lat/lng) Friday, 12 April 13
  65. 65. Example App • Put it all together: • Open Data • PostGIS • CRS transformations • Geospatial DB queries Friday, 12 April 13
  66. 66. Friday, 12 April 13
  67. 67. GeoPostCoder • https://github.com/gavinheavyside/ geopostcoder • Bash and SQL to load postcode geo data • Simple Ruby web app to query DB Friday, 12 April 13
  68. 68. Loading Data • Filter Code-Point Open just to the columns we want • Load into a temporary table • Transform National Grid coordinates to WGS Geography data type Friday, 12 April 13
  69. 69. Friday, 12 April 13
  70. 70. Friday, 12 April 13
  71. 71. Friday, 12 April 13
  72. 72. Friday, 12 April 13
  73. 73. Friday, 12 April 13
  74. 74. Recap • Lots of sources of location data • You probably have a GPS receiver with you • Lots of data available for free • Plenty of free and open-source tools querying and manipulating spatial data • Go do something interesting with it :) Friday, 12 April 13
  75. 75. @gavinheavyside gavin@heavyside.co.uk Friday, 12 April 13

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