Distributed GIS - Geotagging

Geotagging

Geotagging is the process of adding geographical identification metadata to resources such as websites, RSS feed, images or videos. The metadata usually consist of latitude and longitude coordinates but may also include altitude, camera holding direction, place information and so on. Flickr website is one of the famous web services which host photos and provides functionality to add latitude and longitude information to the picture.

The main idea is to use metadata related to pictures and photo collection. A geotag is simply a properly-formed XML tag giving the geographic coordinates of a place. The coordinates can be specified in latitude and longitude or in UTM (Universal Transverse Mercator) coordinates. The RDFIG Geo vocabulary from the W3C is the common basis for the recommendations. It supplies official global names for the latitude, longitude, and altitude properties. These are given in a system of coordinates known as "the WGS84 datum". (A geographic datum specifies an ellispoidal approximation to the Earth's surface; WGS84 is the most commonly used such datum; it is utilized, e.g. for GPS).

To specify that the longitude of something is X, that its latitude is Y, and, optionally, that its altitude is Z, tags form of the tags used is X Y Z

Altitude is specified in meters. The prefix "geo:" represents the RDFIG Geo namespace, whose URL is: http://www.w3.org/2003/01/geo/wgs84_pos#.

Geotagging an HTML element

The following tag will pass muster as correct XML in the context of XHTML (the newer dialect of HTML that adheres to the XML standard), but will also work in earlier HTML dialects, in the sense of being tolerated by all modern browsers. To geotag an HTML element, include a span of the following form:

If the geo namespace is defined at an outer level of the document, the namespace definition in the span tag can be omitted, leaving 46.1124 In earlier HTML dialects, omitting the namespace definition is also appropriate, since the objective of adhering to the XML standard is irrelevant. This technique can be used to geotag a post in a weblog, or elements within any HTML document. Geotagging XML (including RSS and RDF).

In XML simply elements of the form

are included as children of the element one wish to tag, and place the definition of the geo namespace at the outermost level of the document. Geotagging a web page Following method is used to assign a location to a web page as a whole, rather than to its parts. In the