Keyhole Markup Language
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Categories: Articles needing additional references from January 2008 | XML-based standards | Google | Keyhole Markup Language | Markup languages | GIS file formats
Keyhole Markup Language (KML) is an XML-based language schema for expressing geographic annotation and visualization on existing or future web-based online maps (2d) and earth browsers (3d). KML was developed for use with Google Earth, which was originally named Keyhole. It was created by Keyhole, Inc, which was acquired by Google in 2004. The name "Keyhole" is an homage to the KH reconnaissance satellites, the original eye-in-the-sky military reconnaissance system first launched in 1976. The KML file specifies a set of features (placemarks, images, polygons, 3D models, textual descriptions, etc.) for display in Google Earth, Maps and Mobile, or any other 3D earth browser (geobrowser) 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". KML shares some of the same structural grammar as GML[1]. Some KML information cannot be viewed in Google Maps or Mobile [2]. KML files are very often distributed as KMZ files, which are zipped KML files with a .kmz extension. When a KMZ file is unzipped, a single "doc.kml" is found along with any overlay and icon images referenced in the KML. Example KML document:
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://earth.google.com/kml/2.0">
<Placemark>
<description>New York City</description>
<name>New York City</name>
<Point>
<coordinates>-74.006393,40.714172,0</coordinates>
</Point>
</Placemark>
</kml>
The MIME type associated to KML is application/vnd.google-earth.kml+xml.
Geodetic reference systems in KMLFor its reference system, KML uses geographic coordinates (latitude and longitude) in the World Geodetic System of 1984 (WGS84). However it does not support the general idea of the geodetic reference system, in which there are multiple coordinate systems of the Earth for which geographic coordinates could be defined. It therefore can not be used for professional purposes in Geomatics or Geodesy. OGC standard processThe KML 2.2 specification has been submitted to the Open Geospatial Consortium to assure its status as an open standard for all geobrowsers. As of November 2007, the OGC has a new KML 2.2 Standards Working Group. Comments were sought on the proposed standard until January 4 2008.[1] Applications using KML
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