Changes between Version 2 and Version 3 of Help/Concepts/Coordinates


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Timestamp:
2014-10-23T18:07:50+02:00 (10 years ago)
Author:
skyper
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interwiki links

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  • Help/Concepts/Coordinates

    v2 v3  
    11[[TranslatedPages(outdated=This page is partly incomplete and outdated.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)]]
    33
    44= Understanding JOSM Coordinates =
    … …  
    66== Openstreetmap coordinates ==
    77
    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.
     8Openstreetmap 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.
    99
    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.
     10The 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.
    1111
    1212== Editor coordinates ==
    1313
    1414=== 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.
     15To 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.
    1616
    1717When 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.
    … …  
    3636=== Projection ===
    3737
    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.
     38The 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.
    3939
    4040The projections are defined in classes in [source:/trunk/src/org/openstreetmap/josm/data/projection org.openstreetmap.josm.data.projection].
    … …  
    5252==== Mercator ====
    5353
    54 The cylindrical [http://en.wikipedia.org/wiki/Mercator_projection Mercator] projection, named after its inventor,
     54The cylindrical [https://en.wikipedia.org/wiki/Mercator_projection Mercator] projection, named after its inventor,
    5555maps meridians and parallels straight and perpendicular.
    5656
    … …  
    6666==== EPSG:4326 ====
    6767
    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.
    6969
    7070(discuss need for WMS servers / Landsat and Yahoo Sat usage)
    … …  
    7272==== UTM ====
    7373
    74 The [http://en.wikipedia.org/wiki/Transverse_Mercator_projection Transverse Mercator] projection is an adaptation of the Mercator projection,
     74The [https://en.wikipedia.org/wiki/Transverse_Mercator_projection Transverse Mercator] projection is an adaptation of the Mercator projection,
    7575rotating the cylinder 90°.
    7676
    77 The [http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system Universal Transverse Mercator] (UTM) with its 60 zones, as well as a number
     77The [https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system Universal Transverse Mercator] (UTM) with its 60 zones, as well as a number
    7878of national grid reference systems, are based on this projection.
    7979
    8080Within 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]
     81typically given in [https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system#Locating_a_position_using_UTM_coordinates Eastings and Northings]
    8282as a meter value from a particular point of origin.  These Eastings and Northings must not be confused with the EastNorth coordinate within JOSM.
    8383