Changes between Version 2 and Version 3 of Help/Concepts/Coordinates
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- 2014-10-23T18:07:50+02:00 (10 years ago)
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Help/Concepts/Coordinates
v2 v3 1 1 [[TranslatedPages(outdated=This page is partly incomplete and outdated. See EPSG:4326 and the proj4 plugin exists !)]] 2 [[ TOC(inline)]]2 [[PageOutline(1-10,Table of Contents)]] 3 3 4 4 = Understanding JOSM Coordinates = … … 6 6 == Openstreetmap coordinates == 7 7 8 Openstreetmap uses Latitude/Longitude coordinates in the [http ://en.wikipedia.org/wiki/World_Geodetic_System WGS84] [http://en.wikipedia.org/wiki/Geodetic_datum geodetic datum] (being compatible with GPS) for its [http://wiki.openstreetmap.org/wiki/Data_Primitives#Node nodes], stored in decimal degree notation with 7 decimal places in the [http://wiki.openstreetmap.org/wiki/.osm .osm] XML files.8 Openstreetmap uses Latitude/Longitude coordinates in the [https://en.wikipedia.org/wiki/World_Geodetic_System WGS84] [https://en.wikipedia.org/wiki/Geodetic_datum geodetic datum] (being compatible with GPS) for its [osmwiki:Data_Primitives#Node nodes], stored in decimal degree notation with 7 decimal places in the [osmwiki:.osm .osm] XML files. 9 9 10 The same spot on earth would have slightly different Latitude/Longitude values in other coordinate systems, depending on the respective [http ://en.wikipedia.org/wiki/Reference_ellipsoid reference ellipsoid] and reference points being used.10 The same spot on earth would have slightly different Latitude/Longitude values in other coordinate systems, depending on the respective [https://en.wikipedia.org/wiki/Reference_ellipsoid reference ellipsoid] and reference points being used. 11 11 12 12 == Editor coordinates == 13 13 14 14 === Java === 15 To render nodes and ways on the rectangular, flat computer screen, the location of the nodes needs to be reversibly mapped into a [http ://en.wikipedia.org/wiki/Cartesian_coordinates cartesian] coordinate system, i.e. having perpendicular axes. JOSM uses the [http://java.sun.com/docs/books/tutorial/2d/overview/index.htm Java 2D graphics API] to take care of the rendering process. The Java API implements the concept of a [http://java.sun.com/docs/books/tutorial/2d/overview/coordinate.html user space] that could be understood as a large canvas with an origin (0,0) in the top left corner, and virtually infinite extension to the right (x) and down (y). Java 2D supports both integers and single or double precision float variables for the (x,y) pair.15 To render nodes and ways on the rectangular, flat computer screen, the location of the nodes needs to be reversibly mapped into a [https://en.wikipedia.org/wiki/Cartesian_coordinates cartesian] coordinate system, i.e. having perpendicular axes. JOSM uses the [http://java.sun.com/docs/books/tutorial/2d/overview/index.htm Java 2D graphics API] to take care of the rendering process. The Java API implements the concept of a [http://java.sun.com/docs/books/tutorial/2d/overview/coordinate.html user space] that could be understood as a large canvas with an origin (0,0) in the top left corner, and virtually infinite extension to the right (x) and down (y). Java 2D supports both integers and single or double precision float variables for the (x,y) pair. 16 16 17 17 When displaying an area from this virtual canvas to the limited device space, the screen window in this case, Java internally converts these (x,y) coordinates to screen coordinates, automatically during rendering. … … 36 36 === Projection === 37 37 38 The reversible mapping from LatLon coordinates to a flat map or the flat computer screen is a [http ://en.wikipedia.org/wiki/Map_projection projection]. JOSM supports a number of different projections because they have different use cases, in particular in the representation of shapes or the usage of different source material which comes already projected, such as printed maps, land registry data, satellite imagery, WMS servers, etc. to be traced over. Some WMS servers may support a variety of projections on request, others are limited to a specific one.38 The reversible mapping from LatLon coordinates to a flat map or the flat computer screen is a [https://en.wikipedia.org/wiki/Map_projection projection]. JOSM supports a number of different projections because they have different use cases, in particular in the representation of shapes or the usage of different source material which comes already projected, such as printed maps, land registry data, satellite imagery, WMS servers, etc. to be traced over. Some WMS servers may support a variety of projections on request, others are limited to a specific one. 39 39 40 40 The projections are defined in classes in [source:/trunk/src/org/openstreetmap/josm/data/projection org.openstreetmap.josm.data.projection]. … … 52 52 ==== Mercator ==== 53 53 54 The cylindrical [http ://en.wikipedia.org/wiki/Mercator_projection Mercator] projection, named after its inventor,54 The cylindrical [https://en.wikipedia.org/wiki/Mercator_projection Mercator] projection, named after its inventor, 55 55 maps meridians and parallels straight and perpendicular. 56 56 … … 66 66 ==== EPSG:4326 ==== 67 67 68 [http ://en.wikipedia.org/wiki/EPSG:4326 EPSG:4326] is a common Lat/Lon coordinate reference system that refers to WGS84.68 [https://en.wikipedia.org/wiki/EPSG:4326 EPSG:4326] is a common Lat/Lon coordinate reference system that refers to WGS84. 69 69 70 70 (discuss need for WMS servers / Landsat and Yahoo Sat usage) … … 72 72 ==== UTM ==== 73 73 74 The [http ://en.wikipedia.org/wiki/Transverse_Mercator_projection Transverse Mercator] projection is an adaptation of the Mercator projection,74 The [https://en.wikipedia.org/wiki/Transverse_Mercator_projection Transverse Mercator] projection is an adaptation of the Mercator projection, 75 75 rotating the cylinder 90°. 76 76 77 The [http ://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system Universal Transverse Mercator] (UTM) with its 60 zones, as well as a number77 The [https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system Universal Transverse Mercator] (UTM) with its 60 zones, as well as a number 78 78 of national grid reference systems, are based on this projection. 79 79 80 80 Within UTM zones or the national grid systems, a reference of 2-dimensional cartesian coordinates can be defined, 81 typically given in [http ://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system#Locating_a_position_using_UTM_coordinates Eastings and Northings]81 typically given in [https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system#Locating_a_position_using_UTM_coordinates Eastings and Northings] 82 82 as a meter value from a particular point of origin. These Eastings and Northings must not be confused with the EastNorth coordinate within JOSM. 83 83