1. GIS: conceptual reminder Franck Theeten – Bart Meganck

2. Earth’s Grid System Coordinates are usually noted in a Cartesian reference system (with 2 axes, bi-dimensional) 0 1 23 4 56 1 4 3 X Y

3. Earth’s Grid System Note: the unit for measurements doesn’t depend from the axes, but from the reference system (it can be degrees, but also meter, 0 1 23 4 56 1 4 3 X Y

4. Earth’s Grid System Note: the unit for measurements doesn’t depend from the axes, but from the reference system : – Reference system is combination of – geoid (real earth surface) – Ellipsoid (mathematical approximation of earth volume) – Shape and position of projection plane – Origin of the 2 axes – Unit of measurement (can be degrees or meter)

5. Latitude and longitude longitude (meridians) latitude (parallels)

6. the easy part : latitude Determine the angle between a position and the earth axis (plane of the equator) Not affected by earth rotation Can be measured by comparing angles between the soil and the light coming from the Sun

7. the hard part : longitude Value affected by earth rotation Dependent of time (initially calculated by clocks aligned on local noon) Definition of a reference meridian is not physical but arbitrary – Often linked to political reason and colonial history Currently (since the 19 th century: Greenwich, UK) Before, 15 th century: Meridian of Tordesillas (separation between Portuguese and Spanish colonies)

8. the hard part : longitude Value affected by earth rotation Dependent of time (initially calculated by clocks aligned on local noon) Definition of a reference meridian is not physical but arbitrary – Often linked to political reason and colonial history Currently (since the 19 th century: Greenwich, UK) Before, 15 th century: Meridian of Tordesillas (separation between Portuguese and Spanish colonies)

9. Geodesy: measuring earth Old style: physical (plumb line) New style: by satellite

10. Geodesy: measuring earth Old style: physical (plumb line) New style: by satellite

11. Physical geodesy Spirit level /plumb line Theodolite (angles)‏ rope/tape measure (distances)‏ ==> LOCAL gravity

12. Physical geodesy The GEOID : sum object of all local gravity fields (plumb line)

13. The Geoid Sum of local gravities, VERY complex Not related to altitude

14. Satellite geodesy Geoid is not used Gravity center of Earth is only point that sattellites can “feel”, they know nothing about Earth's surface Mathematical model for Earth surface : ELLIPSOID

15. The ELLIPSOID Mathematical model for Earth surface Approximation, never exact ! Not a perfect sphere (1/300 flattening)

16. Geodetic DATUM A geodetic datum is a physical realization of a coordinate system used for describing point locations Contain ALL parameters for your reference system

17. Mention the DATUM ! ! ! Mention the DATUM ! ! !

18. ALWAYS mention the DATUM Coordinates without datum are UTTERLY USELESS !!! Coordinates without datum are UTTERLY MEANINGLESS !!! Coordinates without datum are COMPLETE NONSENSE !!!

19. Well Known Text notation (WKT) A) coordinates B) Projection Type « POINT(X Y) » Ex : -POINT(0 0) -LINESTRING(0 0, 1 1, 1 2) -POLYGON (0 0, 1 1, 1 2, 0 0) - … PROJCS["NAD83 / UTM Zone 10N", GEOGCS["NAD83", DATUM["North_American_Datum_1983", SPHEROID["GRS 1980",6378137,298.257222101] ], PRIMEM["Greenwich",0], UNIT["degree",0.0174532925199433] ], PROJECTION["Transverse_Mercator"], PARAMETER["latitude_of_origin",0], PARAMETER["central_meridian",-123], PARAMETER["scale_factor",0.9996], PARAMETER["false_easting",500000], PARAMETER["false_northing",0], UNIT["metre",1] ]

20. Well Known Text for projection An important reference: http://spatialreference.org/ Gives the GDAL expression of some projections that are not embedded by default in tools like QGIS or PostGIS

21. QGIS: changing the projection settings

22. Tick this box

23. QGIS: changing the projection settings Select the projection by categories Select the projection by name

24. Quantum GIS: define custom projection

25. Projections

26. Plate Carrée EPSG:4326 is the default projection of many applicatio, data (GPS, Shapefile) for WGS 84 Doesn’t prevent local deformation of distances and areas (North appears bigger than equatorial region) Plate Carrée

27. Simple Mercator

28. Simple Mercator/Plate Carrée Conserves angles Distorts surfaces Distortion at the poles

29. Simple Mercator/Plate Carrée Conserves angles Distorts surfaces Distortion at the poles

30. Gall-Peeters map type

31. Conserves surfaces Distorts angles

32. Universal Transverse Mercator Network of projection arranged by longitude Cylindrical

33. Universal Transverse Mercator Looks a “disco ball” (select small rectangular areas to limit deformation of areas, distances and angles to minimal)

34. UTM Zones

35. Interest: unit is meter (distance are easy to express) But each zone has its own local origin (not bound to the equator) Most of time cannot be applied on world scale layers

36. UTM Zones Transerve

37. UTM Data Pretty much use for Raster data – elevation data (SRTM) – http://srtm.csi.cgiar.org/ http://srtm.csi.cgiar.org/ – http://www.cgiar-csi.org/data/srtm-90m-digital-elevation- database-v4-1 http://www.cgiar-csi.org/data/srtm-90m-digital-elevation- database-v4-1 – Climatic data – Processed satellite images (LANDSAT) – https://zulu.ssc.nasa.gov/mrsid https://zulu.ssc.nasa.gov/mrsid

38. Type of data

39. Types of data for GIS Vector data Raster data

40. Vector data Vector layer: – Mathematical expression of a geographical shape points, lines, surfaces – Easy to reproject (parameter of equation) – Already georeferenced – ESRI Shapefile most common data standard for shapefiles

41. Vector data (shapefile) A shapefile: – Elaborated by ESRI but widely used at least 3 (or event better 4) files with the same name but different extensions that must be out in the same folder

42. Vector data (shapefile) ***.shp => the shape (drawn form) ***.dbf => attribute table (editable in spreadsheet) ***.shx=>intermediate index ***.prj=> Metadata of the projection (WKT format)

43. Raster data Image file or grid used to display matricial data Need georefencing project Hard to reproject QGIS can reproject them Most common standard for Images Altitude data (DEM: Digital Elemevation model: http://www.cgiar-csi.org/data/elevation/item/45-srtm-90m-digital-elevation-database-v41 ) http://www.cgiar-csi.org/data/elevation/item/45-srtm-90m-digital-elevation-database-v41 Climatic data http://www.worldclim.org/download http://www.worldclim.org/download

44. Types of GIS application

45. 1) Desktop GIS Can produce, update verctor and raster data Can work without Internet connection Required to procude the base data (backbone of GIS) Example: – QuantumGIS, Diva-GIS (free) – MapInfo, ESRI ArcINFO (commercial) – …

46. 1) Desktop GIS Can produce, update verctor and raster data Can work without Internet connection Required to procude the base data (backbone of GIS) Can not publish data on the Internet Generally poor metadata support Example: – QuantumGIS, Diva-GIS (free) – MapInfo, ESRI ArcINFO (commercial) – …

47. 2) GIS database Relational databases with plugins to handle geographical data No Graphical interface (but Desktop GIS can connect them and display content) Originally worked on vectors, but soince recently can handle rasters and 3-D data Powerful to store and modify big vector datasets Useful to store maps displayed on the Internet

48. 2) GIS database Example: – PostGIS (GIS plug-in of the OpenSource PostgreSQL database)

49. 3) GIS web services Services to displayus the maps on the Internet application Standardized by Open Geospatial Consortium (a.o. Web Map Server: map are queried via the URL) Data are often stored in GIS databases At this level data can easily be completed by metadata

50. 3) GIS web services Example: – GeoServer (Open source): map server http://geoserver.org – GeoNetwork (OpenSpource, created by FAO): metadata server http://geonetwork-opensource.org/

51. 3) GIS web services Example: – GeoServer (Open source): map server http://geoserver.org – GeoNetwork (OpenSpource, created by FAO): metadata server http://geonetwork-opensource.org/ – OpenLayers: Javascript library to integrate maps in web pages http://www.openlayers.org/

52. Client on the Internet Server Scientist computer 3) Typical architecture for Web GIS Maps and data Database and query engines Maps and search interfaces

53. Client on the Internet Server Scientist computer 3) Typical architecture for Web GIS Shapefile or rasters HTTP server (often Tomcat for Java) Map server (GeoServer) Metadata server (Geonetwork) Web page with Javascript client (OpenLayers) GIS database (PostGIS) Imported (QGIS, OGR, GDAL)