tirsdag den 17. marts 2009

Technical Overview: GeoRSS




GeoRSS is a standard for adding location information to an RSS feed. Example applications include travel blogs, news feeds, and real time earthquake feeds. Location information is typically a point location, but it can also include geographic lines, polygons, and related feature descriptions. Many online mapping services support GeoRSS, allowing map "mashups" to be easily created.

GeoRSS currently has three different vocabularies: Simple, GML, and W3C Geo. All three vocabularies can be inserted into RSS 1.0, RSS 2.0, and Atom feeds. Although the GeoRSS model is usually serialized as XML, it can also be serialized as RDF or XHTML.
GeoRSS currently uses a fixed coordinate system of decimal longitude, latitude degrees using the global WGS84 geoid. This is the same as most online map services, and allows for "mashups" without the need for messy coordinate transformations.

The GeoRSS model geometry supports points, lines and boundaries. Boundaries, in turn, can be polygons (with four or more coordinate pairs) or boxes. A box is defined with two longitude, latitude coordinates that define the south-west and north-east corners of a compass-aligned box.

The GeoRSS model also supports the featuretypetag that stores a single string determining the feature's type referred in the geometry. The default is "location". Another single string tag is relationshiptag. This relates the GeoRSS feature to the parent tag. The default is "is-located-at".

The Simple vocabulary also supports two tags for elevation information. elev provides the height in meters above the WGS84 ellipsoid. floor is intended to store a building floor number. The floor number has cultural variations, but should be unambiguous because the building's location is known. [...]

Simple Vocabulary

The Simple vocabulary was designed to be concise, and only requires a single tag per GeoRSS object. The conciseness means that the Simple vocabulary does not have a direct upward compatibility with the GML vocabulary, but automated transformations are possible.

The Simple vocabulary uses the georss namespace. An example Simple tag for a line would be:  [...]

45.2 -105.0 45.3 -110.0 48.1 -115 45.1 -120 

Read more: http://www.geowebguru.com/articles/108-technical-overview-georss

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