Slides from my ACCU2013 talk on location, GPS, GIS and PostGIS.

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
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5. • www.mydrivesolutions.com
• Insurance telematics
• Linux,Ruby, Rails, Postgres, PostGIS,
NoSQL, Chef, AWS, C++
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7. • I have no idea what I’m doing
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8. GPS
• Currently 32 satellites
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9. GPS
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10. Basic GPS Concepts
• 24+ Satellites orbit the earth
• Atomic clocks
• Each constantly transmits its time and
location
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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
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12. http://www.ausairpower.net/TE-GPS-Guided-Weps.html
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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
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14. NMEA 0183
• Serial ASCII data format
• CSV ‘sentences’ for different types of data
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15. NMEA Sentences
• GGA - Fix information
• GSA - DOP and active satellites
• GSV - Satellites in view
• RMC - Time, date and position
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17. Problems with GPS
• Noise
• Urban Canyons
• Multipath signals
• Solar flares and atmospherics
• Mounting of receiver
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18. Others
• GLONASS
• BEIDOU/COMPASS
• GALILEO
• IRNSS
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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
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20. HTML5 GeoLocation
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22. Digital Maps
• Commercial
• NAVTEQ, Tele Atlas
• Free
• OSM
• Online
• Google, Bing, etc
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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
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24. Leaflet
• JS plugin
• Uses OSM or other tile servers
• HW accelerated, touch-compatible
• Markers, Polygons, Layers, GeoJSON
• http://leafletjs.com
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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
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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
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30. • Some people when faced with a problem
think “I know, I’ll use XML”. Now they have
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31. Data Formats
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32. Geometry Types
• Points
• Linestrings
• Polygons
• Compound: MultiPoint etc
• 3D: all above with elevation, Polyhedrals
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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)
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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))
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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
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36. KML
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38. GeoJSON
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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
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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
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42. Geoid
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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
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45. Projections
• Projections • Orientation
• Cylindrical • Oblique
• Conic • Equatorial
• Azimuthal • Transverse
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46. Transverse Mercator
• Some projections look good over most of
the globe
• Some are only useful locally (e.g. UTM)
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47. Geospatial Databases
• Ordinary RDBs with support for spatial
data types
• NoSQL DBs
• MongoDB
• https://github.com/neo4j/spatial
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48. PostGIS
• http://postgis.org/
• Geospatial Extensions for PostgreSQL
• Excellent support for spatial data,
operations, indexes
• Actively developed
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49. Creating a PostGIS DB
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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
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51. ST_Equals
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52. ST_Intersects
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53. ST_DWithin
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54. ST_Transform
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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
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56. Geospatial Indexes
• Indexes on geo columns are necessary
• Covers bounding boxes
• Reduces search space
• Geos used for calculations
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57. EXPLAIN
• Use EXPLAIN to check the planner is using
spatial indexes, just like other SQL queries
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58. Ordnance Survey
OpenData
• http://www.ordnancesurvey.co.uk/
oswebsite/products/os-opendata.html
• Vector & Raster data
• Maps, Roads, Boundaries, Postcodes
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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
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61. Data Format
• Postcode in field 1
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62. Data Format
• Eastings, Northings in fields 3,4
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63. OS National Grid
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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)
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65. Example App
• Put it all together:
• Open Data
• PostGIS
• CRS transformations
• Geospatial DB queries
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67. GeoPostCoder
• https://github.com/gavinheavyside/
geopostcoder
• Bash and SQL to load postcode geo data
• Simple Ruby web app to query DB
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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
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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 :)
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75. @gavinheavyside
gavin@heavyside.co.uk
Friday, 12 April 13