Location Location Location

Location Location Location

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  Location Location Location Gavin Heavyside - ACCU 2013 - 12 April 2012 gavin@heavyside.co.uk @gavinheavyside Friday, 12 April 13
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  GPS, Location, GIS,and Spatial Relationships • GPS Technology • GIS and Mapping Concepts • Spatial DBs and SQL • Practical Example Friday, 12 April 13
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  • www.mydrivesolutions.com • Insurance telematics • Linux,Ruby, Rails, Postgres, PostGIS, NoSQL, Chef, AWS, C++ Friday, 12 April 13
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  • I haveno idea what I’m doing Friday, 12 April 13
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  GPS • Currently 32 satellites Friday, 12 April 13
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  GPS Friday, 12 April13
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  Basic GPS Concepts • 24+ Satellites orbit the earth • Atomic clocks • Each constantly transmits its time and location Friday, 12 April 13
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  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
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  http://www.ausairpower.net/TE-GPS-Guided-Weps.html Friday, 12 April13
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  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
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  NMEA 0183 • Serial ASCII data format • CSV ‘sentences’ for different types of data Friday, 12 April 13
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  NMEA Sentences • GGA - Fix information • GSA - DOP and active satellites • GSV - Satellites in view • RMC - Time, date and position Friday, 12 April 13
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  Problems with GPS • Noise • Urban Canyons • Multipath signals • Solar flares and atmospherics • Mounting of receiver Friday, 12 April 13
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  Others • GLONASS • BEIDOU/COMPASS • GALILEO • IRNSS Friday, 12 April 13
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  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
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  HTML5 GeoLocation Friday, 12April 13
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  Digital Maps • Commercial • NAVTEQ, Tele Atlas • Free • OSM • Online • Google, Bing, etc Friday, 12 April 13
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  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
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  Leaflet • JS plugin • Uses OSM or other tile servers • HW accelerated, touch-compatible • Markers, Polygons, Layers, GeoJSON • http://leafletjs.com Friday, 12 April 13
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  Digital maps forGIS • 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
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  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
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  • Some peoplewhen faced with a problem think “I know, I’ll use XML”. Now they have Friday, 12 April 13
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  Data Formats Friday, 12April 13
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  Geometry Types • Points • Linestrings • Polygons • Compound: MultiPoint etc • 3D: all above with elevation, Polyhedrals Friday, 12 April 13
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  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
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  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
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  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
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  KML Friday, 12 April13
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  GeoJSON Friday, 12 April13
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  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
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  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
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  Geoid Friday, 12 April13
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  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
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  Projections • Projections • Orientation • Cylindrical • Oblique • Conic • Equatorial • Azimuthal • Transverse Friday, 12 April 13
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  Transverse Mercator • Some projections look good over most of the globe • Some are only useful locally (e.g. UTM) Friday, 12 April 13
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  Geospatial Databases • Ordinary RDBs with support for spatial data types • NoSQL DBs • MongoDB • https://github.com/neo4j/spatial Friday, 12 April 13
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  PostGIS • http://postgis.org/ • Geospatial Extensions for PostgreSQL • Excellent support for spatial data, operations, indexes • Actively developed Friday, 12 April 13
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  Creating a PostGISDB Friday, 12 April 13
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  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
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  ST_Equals Friday, 12 April13
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  ST_Intersects Friday, 12 April13
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  ST_DWithin Friday, 12 April13
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  ST_Transform Friday, 12 April13
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  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
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  Geospatial Indexes • Indexes on geo columns are necessary • Covers bounding boxes • Reduces search space • Geos used for calculations Friday, 12 April 13
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  EXPLAIN • Use EXPLAIN to check the planner is using spatial indexes, just like other SQL queries Friday, 12 April 13
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  Ordnance Survey OpenData • http://www.ordnancesurvey.co.uk/ oswebsite/products/os-opendata.html • Vector & Raster data • Maps, Roads, Boundaries, Postcodes Friday, 12 April 13
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  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
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  Data Format • Postcode in field 1 Friday, 12 April 13
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  Data Format • Eastings, Northings in fields 3,4 Friday, 12 April 13
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  OS National Grid Friday,12 April 13
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  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
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  Example App • Put it all together: • Open Data • PostGIS • CRS transformations • Geospatial DB queries Friday, 12 April 13
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  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
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  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
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  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
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  @gavinheavyside gavin@heavyside.co.uk Friday, 12 April 13