Location Location Location

1. Location Location Location Gavin Heavyside - ACCU 2013 - 12 April 2012 gavin@heavyside.co.uk @gavinheavyside Friday, 12 April 13

2. Friday, 12 April 13

3. GPS, Location, GIS, and Spatial Relationships • GPS Technology • GIS and Mapping Concepts • Spatial DBs and SQL • Practical Example Friday, 12 April 13

5. • www.mydrivesolutions.com • Insurance telematics • Linux,Ruby, Rails, Postgres, PostGIS, NoSQL, Chef, AWS, C++ Friday, 12 April 13

7. • I have no idea what I’m doing Friday, 12 April 13

8. GPS • Currently 32 satellites Friday, 12 April 13

9. GPS Friday, 12 April 13

10. Basic GPS Concepts • 24+ Satellites orbit the earth • Atomic clocks • Each constantly transmits its time and location Friday, 12 April 13

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. http://www.ausairpower.net/TE-GPS-Guided-Weps.html Friday, 12 April 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. NMEA 0183 • Serial ASCII data format • CSV ‘sentences’ for different types of data Friday, 12 April 13

15. NMEA Sentences • GGA - Fix information • GSA - DOP and active satellites • GSV - Satellites in view • RMC - Time, date and position Friday, 12 April 13

17. Problems with GPS • Noise • Urban Canyons • Multipath signals • Solar ﬂares and atmospherics • Mounting of receiver Friday, 12 April 13

18. Others • GLONASS • BEIDOU/COMPASS • GALILEO • IRNSS Friday, 12 April 13

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. HTML5 GeoLocation Friday, 12 April 13

22. Digital Maps • Commercial • NAVTEQ, Tele Atlas • Free • OSM • Online • Google, Bing, etc Friday, 12 April 13

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. Leaﬂet • JS plugin • Uses OSM or other tile servers • HW accelerated, touch-compatible • Markers, Polygons, Layers, GeoJSON • http://leaﬂetjs.com Friday, 12 April 13

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. 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

30. • Some people when faced with a problem think “I know, I’ll use XML”. Now they have Friday, 12 April 13

31. Data Formats Friday, 12 April 13

32. Geometry Types • Points • Linestrings • Polygons • Compound: MultiPoint etc • 3D: all above with elevation, Polyhedrals Friday, 12 April 13

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. 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. 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. KML Friday, 12 April 13

38. GeoJSON Friday, 12 April 13

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

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. Geoid Friday, 12 April 13

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

45. Projections • Projections • Orientation • Cylindrical • Oblique • Conic • Equatorial • Azimuthal • Transverse Friday, 12 April 13

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. Geospatial Databases • Ordinary RDBs with support for spatial data types • NoSQL DBs • MongoDB • https://github.com/neo4j/spatial Friday, 12 April 13

48. PostGIS • http://postgis.org/ • Geospatial Extensions for PostgreSQL • Excellent support for spatial data, operations, indexes • Actively developed Friday, 12 April 13

49. Creating a PostGIS DB Friday, 12 April 13

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. ST_Equals Friday, 12 April 13

52. ST_Intersects Friday, 12 April 13

53. ST_DWithin Friday, 12 April 13

54. ST_Transform Friday, 12 April 13

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. Geospatial Indexes • Indexes on geo columns are necessary • Covers bounding boxes • Reduces search space • Geos used for calculations Friday, 12 April 13

57. EXPLAIN • Use EXPLAIN to check the planner is using spatial indexes, just like other SQL queries Friday, 12 April 13

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

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. Data Format • Postcode in ﬁeld 1 Friday, 12 April 13

62. Data Format • Eastings, Northings in ﬁelds 3,4 Friday, 12 April 13

63. OS National Grid Friday, 12 April 13

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. Example App • Put it all together: • Open Data • PostGIS • CRS transformations • Geospatial DB queries Friday, 12 April 13

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. 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

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. @gavinheavyside gavin@heavyside.co.uk Friday, 12 April 13

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