Keyhole Markup Languagekeyhole markup language, keyhole markup language using spreadsheets
Keyhole Markup Language KML is an XML notation for expressing geographic annotation and visualization within Internet-based, two-dimensional maps and three-dimensional Earth browsers KML was developed for use with Google Earth, which was originally named Keyhole Earth Viewer It was created by Keyhole, Inc, which was acquired by Google in 2004 KML became an international standard of the Open Geospatial Consortium in 2008 Google Earth was the first program able to view and graphically edit KML files Other projects such as Marble have also started to develop KML support
- 1 Structure
- 2 Geodetic reference systems in KML
- 3 OGC standard process
- 4 See also
- 5 References
- 6 External links
The KML file specifies a set of features place marks, images, polygons, 3D models, textual descriptions, etc for display in Here Maps, Google Earth, Maps and Mobile, or any other geospatial software implementing the KML encoding Each place always has a longitude and a latitude Other data can make the view more specific, such as tilt, heading, altitude, which together define a "camera view" along with a timestamp or timespan KML shares some of the same structural grammar as GML Some KML information cannot be viewed in Google Maps or Mobile
KML files are very often distributed in KMZ files, which are zipped KML files with a kmz extension These must be legacy ZIP 20 compression compatible ie stored or deflate method, otherwise the kmz file might not uncompress in all geobrowsers The contents of a KMZ file are a single root KML document notionally "dockml" and optionally any overlays, images, icons, and COLLADA 3D models referenced in the KML including network-linked KML files The root KML document by convention is a file named "dockml" at the root directory level, which is the file loaded upon opening By convention the root KML document is at root level and referenced files are in subdirectories eg images for overlay images
An example KML document is:<xml version="10" encoding="UTF-8"> <kml xmlns="http://wwwopengisnet/kml/22"> <Document> <Placemark> <name>New York City</name> <description>New York City</description> <Point> <coordinates>-74006393,40714172,0</coordinates> </Point> </Placemark> </Document> </kml>
The MIME type associated with KML is application/vndgoogle-earthkml+xml; the MIME type associated with KMZ is application/vndgoogle-earthkmz
Geodetic reference systems in KML
For its reference system, KML uses 3D geographic coordinates: longitude, latitude and altitude, in that order, with negative values for west, south and below mean sea level if the altitude data is available The longitude, latitude components decimal degrees are as defined by the World Geodetic System of 1984 WGS84 The vertical component altitude is measured in meters from the WGS84 EGM96 Geoid vertical datum If altitude is omitted from a coordinate string, eg -7703647, 3889763 then the default value of 0 approximately sea level is assumed for the altitude component, ie -7703647, 3889763, 0
A formal definition of the coordinate reference system encoded as GML used by KML is contained in the OGC KML 22 Specification This definition references well-known EPSG CRS components
OGC standard process
The KML 22 specification was submitted to the Open Geospatial Consortium to assure its status as an open standard for all geobrowsers In November 2007 a new KML 22 Standards Working Group was established within OGC to formalize KML 22 as an OGC standard Comments were sought on the proposed standard until January 4, 2008, and it became an official OGC standard on April 14, 2008
The OGC KML Standards Working Group is currently working on change requests to KML 22 and incorporating accepted changes into a future KML 23 standard
- Geography Markup Language
- Geospatial content management system
- GPS eXchange Format
- Point of interest
- ^ OGC® Approves KML as Open Standard | OGCR
- ^ Kml | OgcR
- ^ KML Support in Marble
- ^ "Can Google Maps read the KML files I've made for Google Earth" Google Retrieved 2009-06-15
- ^ "Viewing data from Google Earth" Google Retrieved 2013-04-07
- ^ "KMZ Files" Google Retrieved 2009-12-16
- ^ Wilson, Tim, ed 2008-04-14 OGC KML Open Geospatial Consortium, Inc p 14 Retrieved 9 June 2015
- ^ "The OGC Seeks Comment on OGC Candidate KML 22 Standard" Press release Open Geospatial Consortium, Inc 2007-12-04 Retrieved 2007-12-10
- ^ Shankland, Stephen 2008-04-14 "Google mapping spec now an industry standard" CNET Retrieved 2008-04-14
- ^ "OGC KML 23 SWG" OGC Retrieved 2013-10-07
- OGC KML 22 Standard
- OGC Official KML 22 Schema
- Google's KML Documentation
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