The aim of this protocol is to define a method for including location information in an SMS text message.
The method basically involves embedding one or more geo URIs (see below) in the body of an SMS, separated from the message text and each other by one or more spaces. A message containing such a URI is known as a geotagged SMS.
A geo URI is defined in RFC 5870 as follows.
The optional altitude is in metres above sea level, and the optional uncertainty distance u is in metres. The optional coordinate reference scheme crs defaults to WGS-84, as used by GPS.
Here are some examples of geo URIs, with explanatory comments.
geo:-37.801631,144.980294 The location of a pub in Fitzroy
geo:-37.801631,144.980294;u=10 The location of the pub, known to within 10 metres
geo:-37.801631,144.980294,200 The location of the pub, 200 metres above sea level
A geotagged SMS is defined to be an SMS text message containing such a URI. For example.
Meet me at the pub geo:-37.801631,144.980294;u=10
It is also possible to include two or more locations in an SMS. For example.
I’ll be at the pub geo:-37.801631,144.980294;u=10 until midnight, then heading to a gig geo:-37.864225,144.97294
And that’s the GeoSMS protocol.
A few things to note –
- The message text of a geotagged SMS must not contain the four-character sequence “geo:”
- A geo URI should specify an uncertainty distance if it is known.
- The accuracy of the latitude and longitude values in a geo URI in should not exceed six decimal places.
- The default CRS of a geo URI is WGS-84, the reference system used by GPS. URIs should use this default, and receiving applications may ignore other values.
- Applications that send SMS messages should only include the sender’s current location if it is explicitly requested. For privacy reasons, text messages should not be automatically geo-tagged.
- Applications that receive a geo-tagged SMS should display the location information visually, and, where possible, show the locations relative to the receiver’s current position. Possible formats include markers on a map and compass needles with distance counters.
- If you have any questions about the protocol, please post a comment on this blog.