EPSG:3857
From OpenStreetMap Wiki
EPSG:3857 is a Spherical Mercator projection coordinate system popularized by web services such as Google and later OpenStreetMap.
Contents |
Codes
- 54004 - Google Maps uses this projection, in decimal degrees, others meters sometimes (sometimes equivalent?)
- OSGEO:41001 - OSGeo created this code while developing the Tile Map Service (TMS) specification. [1] It was superceded by 900913. (equivalent, deprecated)
- 900913 - Sometimes described as EPSG:900913, this was created for OpenLayers (equivalent)
- ESRI:102113 - First used by ESRI, but then replaced by 102100 (equivalent, deprecated)
- ESRI:102100 - Built differently, but equivalent to 102113 (equivalent, deprecated)
- EPSG:3785 - EPSG added this, similiar to how ESRI:102113 is defined (equivalent, deprecated)
- EPSG:3587 - was never a real EPSG code, but some used this likely as a mistype of EPSG:3785 (mistype)
- EPSG:3857 - EPSG replaced EPSG:3785 with this, and ESRI replaced ESRI:102100 with this (current)
History
- 2007/08/06 - Christopher Schmidt of OpenLayers announces use of the number 900913 to describe the "Google Projection" [2]
- 2007/09/11 - Christopher Schmidt checks in OpenLayers/Layer/SphericalMercator.js with WKID 900913 [3]
- 2003/06/25 (or earlier) - Google (or a user) begins using WKID 54004, either as EPSG:54004 or ESRI:54004 [4]
- 2008/05/?? - EPSG updates mailing list that EPSG:3785 will be added to version 6.15 [5]
- 2009/02/09 - EPSG changed EPSG:3785 to EPSG:3857 [6]
- 2008/08/05 - Google Support thread on the use of Web Mercator in which it's noted (less technically) that the projection formerly used by Google Maps did not preserve azimuth at high latitudes.[7]
- ?? - ESRI ArcGIS 10 changed the WKID for this projection from ESRI:102100 to EPSG:3857 [8]
- 2010/09/15 - Noel Zinn from Hydrometrics gave a presentation at GIS in the Rockies on the mathematical uncertainty introduced by Web Mercator[9]
References
- ↑ http://wiki.osgeo.org/wiki/Tile_Map_Service_Specification#global-mercator
- ↑ http://crschmidt.net/blog/archives/243/google-projection-900913/
- ↑ http://trac.osgeo.org/openlayers/changeset/4221
- ↑ http://johndeck.blogspot.com/2005/09/overlaying-mercator-projected-wms.html
- ↑ http://sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx
- ↑ http://viswaug.wordpress.com/2009/04/01/gis-standards-gone-crazy-epsg-especially/
- ↑ http://www.google.com/support/forum/p/maps/thread?tid=075eb10962e00cc5&hl=en
- ↑ http://forums.arcgis.com/threads/8762-WGS-1984-Web-Mercator-(Auxiliary-Sphere)-WKID-102100?p=27549&viewfull=1#post27549
- ↑ http://www.hydrometronics.com/downloads/Web%20Mercator%20-%20Non-Conformal,%20Non-Mercator%20(notes).pdf
External Links
- Official entry on EPSG Registry
- SpatialReference.org entry, however not as official EPSG code but SR-ORG:6864
- ArcGIS forum discussion on ESRI code history
- ArcGIS forum discussion on the two ESRI codes
- Tiles à la Google Maps: Coordinates, Tile Bounds and Projection - good discussion, including Python code to convert between lat/lon, tiles, pixels, and coordinates (in meters, EPSG:3857)
