GEOPRIV -- Geographic A. Mayrhofer Location/Privacy Working Group nic.at Internet-Draft C. Spanring Expires: August 16, 2009 OIR-ID February 12, 2009 A Uniform Resource Identifier for Geographic Locations ('geo' URI) draft-mayrhofer-geopriv-geo-uri-01 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 16, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document specifies an Uniform Resource Identifier (URI) for Mayrhofer & Spanring Expires August 16, 2009 [Page 1] Internet-Draft 'geo' URI scheme February 2009 geographic locations using the 'geo' scheme name. A 'geo' URI identifies a physical location by latitude, longitude and optionally altitude in a compact, simple, human-readable, and protocol independent way. Table of Contents 1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Registration of 'geo' URI Scheme . . . . . . . . . . . . 6 4.1. URI Scheme Name . . . . . . . . . . . . . . . . . . . . . 6 4.2. Status . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.3. URI Scheme Syntax . . . . . . . . . . . . . . . . . . . . 6 4.4. URI Scheme Semantics . . . . . . . . . . . . . . . . . . . 6 4.4.1. Component Description . . . . . . . . . . . . . . . . 6 4.4.2. URI Comparison . . . . . . . . . . . . . . . . . . . . 7 4.4.3. Interpretation of Undefined Altitude . . . . . . . . . 7 4.5. Encoding Considerations . . . . . . . . . . . . . . . . . 7 4.6. Applications/protocols That Use This URI Scheme . . . . . 8 4.7. Interopability Considerations . . . . . . . . . . . . . . 8 4.8. Security Considerations . . . . . . . . . . . . . . . . . 8 4.9. Contact . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.10. Author/Change controller . . . . . . . . . . . . . . . . . 8 4.11. References . . . . . . . . . . . . . . . . . . . . . . . . 9 5. URI Operations . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Use Cases and Examples . . . . . . . . . . . . . . . . . . . . 9 6.1. Plain 'geo' URI Example . . . . . . . . . . . . . . . . . 9 6.2. Hyperlink . . . . . . . . . . . . . . . . . . . . . . . . 9 6.3. 'geo' URI in 2-dimensional barcode . . . . . . . . . . . . 10 7. GML Mappings . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. 'geo' URI without altitude to GML 'Point' . . . . . . . . 10 7.2. 'geo' URI with Altitude to GML 'Point' . . . . . . . . . . 11 7.3. GML 'Point' without Altitude to 'geo' URI . . . . . . . . 11 7.4. GML 'Point' with Altitude to 'geo' URI . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. Security Considerations . . . . . . . . . . . . . . . . . . . 12 9.1. Invalid Locations . . . . . . . . . . . . . . . . . . . . 12 9.2. Location Privacy . . . . . . . . . . . . . . . . . . . . . 13 Mayrhofer & Spanring Expires August 16, 2009 [Page 2] Internet-Draft 'geo' URI scheme February 2009 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Mayrhofer & Spanring Expires August 16, 2009 [Page 3] Internet-Draft 'geo' URI scheme February 2009 1. Change Log [Note to editors: This section is to be removed before publication - XML source available on request] draft-mayrhofer-geopriv-geo-uri-01 o added terminology text about WGS-84 (credits Carl Reed) o removed "resolution" / "uncertainty" text o added considerations regarding poles o added text about invalid URIs draft-mayrhofer-geopriv-geo-uri-00 o Initial version under new name, reverting to "plain" lat/lon scheme, with the "tiling" scheme moved to seperate draft (potentially published as "draft-mayrhofer-geopriv-geotile-uri"). refer to draft-mayrhofer-geo-uri-01 for the history of this document. o Added GML mapping section draft-mayrhofer-geo-uri-01 o removed parameters draft-mayrhofer-geo-uri-00 o initial draft 2. Introduction An increasing number of Internet protocols and data formats are extended by specifications for adding spatial (geographic) location. In most cases, latitude as well as longitude of simple points are added as new attributes to existing data structures. However, all those methods are very specific to a certain data format or protocol, and don't provide a protocol independent, compact and generic way to refer to a physical geographic location. Over the past few years, fast emerging location aware applications and location based services were observable on the Internet. Most web search engines use geographic information, and a vivid open source mapping community brought an enormous momentum into location aware technology. A wide range and former to professionals exclusive tools and data were provided free of charge for an everyday use on the mass market. The 'geo' URI scheme is another step into that direction and aims to facilitate, support and standardize the problem of location identification in geospatial services and applications. Accessing information about or trigger further services based on a particular Mayrhofer & Spanring Expires August 16, 2009 [Page 4] Internet-Draft 'geo' URI scheme February 2009 place on earth shouldn't be any harder for users than clicking on a 'mailto:' link and write an email straight away. According to [RFC3986], a Uniform Resource Identifier (URI) is "a compact sequence of characters that identifies an abstract or physical resource". The 'geo' URI scheme defined in this document identifies geographic locations (a physical resource) in the World Geodetic System 1984 (WGS-84) [WGS84] reference system. 'Geo' URIs identify a geographic location using a textual representation of the location's spatial coordinates in either two or three dimensions (latitude, longitude, and optionally altitude). Such URIs are independent from a specific protocol, application, or data format, and can be used in any other protocol or data format that supports inclusion of arbitrary URIs. The definition of the URI scheme is strictly focused on the most simplest representation of a spatial location - a single point. The provision of more complex geometries or locations described by civic addresses is out of scope of this document. Note: The choice of WGS-84 is based on the widespread availability of Global Positioning System (GPS) devices, which use the WGS-84 reference system. It is anticipated that such devices serve as one of the primary data sources for authoring 'geo' URIs, hence the adoption of the native GPS reference system for the URI scheme. Also, many other data formats for representing geographic locations use the WGS-84 reference system, which makes transposing from and to such data formats less error prone (no re-projection involved). 3. Terminology Geographic locations in this document are defined using WGS 84 (World Geodetic System 1984), equivalent to the OGP Surveying and Positioning Committee EPSG code 4326 (2 dimensions) and 4979 (3 dimensions). This document does not assign responsibilities for coordinate transformations from and to other Spatial Reference Systems. A 2-dimensional WGS-84 coordinate value is here represented as a comma-delimited latitude/longitude pair, measured in decimal degrees (un-projected). A 3-dimensional WGS-84 coordinate value is here represented by appending a comma-delimited altitude value in meters to such pairs. Latitudes range from -90 to 90 and longitudes range from -180 to 180. Coordinates in the Southern and Western hemispheres as well as Mayrhofer & Spanring Expires August 16, 2009 [Page 5] Internet-Draft 'geo' URI scheme February 2009 altitudes below the WGS-84 reference geoid are signed negative with a leading dash. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 4. IANA Registration of 'geo' URI Scheme This section contains the fields required for the URI scheme registration, following the guidelines in section 5.4 of [RFC4395]. 4.1. URI Scheme Name geo 4.2. Status permanent 4.3. URI Scheme Syntax The syntax of the 'geo' URI scheme is specified below in Augmented Backus-Naur Form (ABNF) [RFC4234]: geo-URI = geo-scheme ":" geo-path geo-scheme = "geo" geo-path = geo-location geo-location = latitude "," longitude [ "," altitude ] latitude = [ "-" ] 1*2DIGIT [ "." *DIGIT ] longitude = [ "-" ] 1*3DIGIT [ "." *DIGIT ] altitude = [ "-" ] *DIGIT [ "." *DIGIT ] 4.4. URI Scheme Semantics Data contained in a 'geo' URI identifies a physical resource: A spatial location on earth in the WGS-84 references system, identified by the geographic coordinates encoded in the URI. 4.4.1. Component Description The "latitude", "longitude" and "altitude" components as specified in the URI scheme syntax ( Section 4.3) are to be used as follows: Mayrhofer & Spanring Expires August 16, 2009 [Page 6] Internet-Draft 'geo' URI scheme February 2009 o The "latitude" component MUST contain the latitude of the identified location in decimal degrees in the reference system WGS-84. o The "latitude" component MUST contain the latitude of the identified location in decimal degrees in the reference system WGS-84. o If present, the OPTIONAL "altitude" component MUST contain the WGS-84 altitude of the identified location in meters. If the altitude of the location is unknown, the "altitude" component MUST NOT be present in the URI. Specifically, unknown altitude MUST NOT be represented by setting the 'altitude' component to "0" (or any other arbitrary value). The "longitude" components of coordinate values reflecting the poles (latitude set to -90 or 90 degrees) SHOULD be set to "0", although consumers of "geo" URIs MUST accept such URIs with any longitude value between -180 and 180. 'geo' URIs with longitude values outside the range of -180 to 180 decimal degrees or with latitude values outside the range of -90 to 90 degrees MUST be considered invalid. 4.4.2. URI Comparison Two 'geo' URIs are equal when their 'longitude', 'latitude' and 'altitude' values are mathematically identical. Where the 'latitude' component of a 'geo' URI is set to either 90 or -90 degrees, the 'longitude' component MUST be ignored in comparison operations. An URI with undefined (missing) 'altitude' value MUST NOT be considered equal to an URI containing an 'altitude' value, even if the remaining values 'latitude' and 'longitude' are equivalent. 4.4.3. Interpretation of Undefined Altitude A consumer of a 'geo' URI with undefined 'altitude' MAY assume that the URI refers to the respective location on earth's physical surface at the given 'latitude' and 'longitude' coordinate. However, as defined above, altitudes are relative to the WGS-84 reference geoid rather than earth's surface. Hence, an altitude value of 0 MUST NOT be interpreted as "on earth's surface". 4.5. Encoding Considerations The 'geo-location' path component of the 'geo' URI (see Section 4.3) uses a comma (",") as a delimiter for subcomponents. This delimiter Mayrhofer & Spanring Expires August 16, 2009 [Page 7] Internet-Draft 'geo' URI scheme February 2009 MUST NOT be percent encoded. It is RECOMMENDED that for readability the contents of 'latitude', 'longitude' and 'altitude' subcomponents are never percent encoded. 4.6. Applications/protocols That Use This URI Scheme As many other URI scheme definitions, the 'geo' URI provides resource identification independent of a specific application or protocol. Examples of potential protocol mappings and use cases can be found in Section 6. 4.7. Interopability Considerations As with any other new URI scheme, the 'geo' URI requires support in client applications. Users of applications which are not aware of the 'geo' scheme are likely unable to make use of the information in the URI. However, the simple structure of the 'geo' URI would even allow manual dereference by users. Poorly authored 'geo' URI instances could contain whitespace and numbers with leading plus signs ("+"). Clients SHOULD try to dereference such URIs after removing such whitespace and plus signs. This specification does not define any URI parameters nor a query component. Future revisions might define such parameters, using the ";" and "?" characters to delimit parameter and query components from the path component specified above. Clients MUST be prepared to encounter such 'geo' URI instances, and MUST reduce the URI to the components specified in Section 4.3 before they dereference the URI. 4.8. Security Considerations See Section 9 of [insert reference to this document] 4.9. Contact Christian Spanring (mailto:spanring@oir.at, http://spanring.eu/ ), Alexander Mayrhofer (mailto:alexander.mayrhofer@nic.at, http://timatio.com/ ) 4.10. Author/Change controller The 'geo' URI scheme is registered under the IETF part of the URI tree. As such, change control is up to the IETF. Mayrhofer & Spanring Expires August 16, 2009 [Page 8] Internet-Draft 'geo' URI scheme February 2009 4.11. References RFC XXXX [change to RFC number once assigned] 5. URI Operations Currently, just one operation on a 'geo' URI is defined - location dereference: In that operation, a client dereferences the URI by extracting the geographical coordinates from the URI path component. Further use of those coordinates is then up to the application processing the URI. An application may then use this location information for various purposes, for example: o A web browser could use that information to open a web mapping service of the user's choice, and display a map of the location o A navigational device such as a Global Positioning System (GPS) receiver could offer the user to start navigation to the location. 6. Use Cases and Examples 6.1. Plain 'geo' URI Example The following 3-dimensional 'geo' URI example references to the office location of one of the authors in Vienna, Austria: geo:48.2010,16.3695,183 A user could type the data extracted from this URI into a electronic navigation device, or even use it to locate the identified location on a paper map. 6.2. Hyperlink 'geo' URIs (like any other URI scheme) could also be embedded as hyperlinks in web pages. A Hyper Text Markup Language (HTML) snippet with such a hyperlink could look like:

one of Vienna's popular sights is the Karlskirche. A web brower could extract the coordinates from the HTML snippet, and offer the user various options (based on configuration, context), for example: Mayrhofer & Spanring Expires August 16, 2009 [Page 9] Internet-Draft 'geo' URI scheme February 2009 o display a small map thumbnail when the mouse pointer hovers over the link o switch to a mapping service of the user's choice once the link is selected o Locate nearby resources, for example by comparing the 'geo' URI with locations extracted from GeoRSS feeds the user has subscribed to. o Convert the coordinates to a format suitable for uploading to a navigation device 6.3. 'geo' URI in 2-dimensional barcode Due to it's short length, a 'geo' URI could easily be encoded in 2-dimensional barcodes. Such barcodes could be printed on business cards, flyers, paper maps and subsequently used by mobile devices, for example as follows: 1. User identifies such a barcode on a flyer, uses the camera on his mobile phone to photograph and decode the barcode 2. The mobile phone dereferences the 'geo' URI, and offers the user to calculate a navigation route to the identified location. 3. Using the builtin GPS, the user follows the navgiation instructions from his phone to reach the destination 7. GML Mappings The Geographic Markup Language (GML) by the Open Geospatial Consortium (OGC) is a set of XML schemas to represent geographical features. Since GML is widely accepted, this document includes instructions on how to transpose 'geo' URIs from and to GML documents. A 'geo' URI can be authored from a GML "point", and any 'geo' URI can be mapped to a GML "point". For the following sections, "%lat%", "%lon%" and "%alt%" are placeholders for latitude, longitude, and altitude values. Mappings are defined as follows: 7.1. 'geo' URI without altitude to GML 'Point' An instance of the 'geo' URI without the altitude element is mapped to a two-dimensional GML "Point" as follows: Mayrhofer & Spanring Expires August 16, 2009 [Page 10] Internet-Draft 'geo' URI scheme February 2009 'geo' URI: geo:%lat%,%lon% GML document: %lat% %lon% 7.2. 'geo' URI with Altitude to GML 'Point' A 'geo' URI instance with the altitude element is mapped to a three- dimensional GML "Point" as follows: 'geo' URI: geo:%lat%,%lon%,%alt% GML document: %lat% %lon% %alt% 7.3. GML 'Point' without Altitude to 'geo' URI A GML 'Point' in the reference system identified as "urn:ogc:def:crs:EPSG:6.6:4326" is mapped to a 'geo' URI as follows: GML document: %lat% %lon% 'geo' URI: geo:%lat%,%lon% Mayrhofer & Spanring Expires August 16, 2009 [Page 11] Internet-Draft 'geo' URI scheme February 2009 Note: GML documents in other reference systems MAY be used as well if a transformation into "urn:ogc:def:crs:EPSG:6.6:4326" is defined and applied before the mapping step. 7.4. GML 'Point' with Altitude to 'geo' URI A GML 'Point' in the reference system identified as "urn:ogc:def:crs:EPSG:6.6:4979" is mapped to a 'geo' URI as follows: GML document: %lat% %lon% 'geo' URI: geo:%lat%,%lon% Note: GML 'Point' instances in other reference systems MAY be used as well if a transformation into "urn:ogc:def:crs:EPSG:6.6:4326" is defined and applied before the mapping step. 8. IANA Considerations This document requests assignment of the 'geo' URI scheme in the IETF part of the URI scheme tree, according to the guidelines in BCP 115 (RFC 4395) [RFC4395]. The definitions required for the assignment are contained in Section 4. 9. Security Considerations Because the 'geo' URI is not tied to any specific protocol, and identifies a physical location rather than a network resource, most of the general security considerations on URIs (Section 7 of RFC 3986) do not apply. However, the following (additional) issues apply: 9.1. Invalid Locations The URI syntax (Section 4.3) makes it possible to construct valid 'geo' URIs which don't identify a valid location on earth. Applications MUST NOT use URIs which such invalid values, and SHOULD Mayrhofer & Spanring Expires August 16, 2009 [Page 12] Internet-Draft 'geo' URI scheme February 2009 warn the user when such URIs are encountered. An example of such an invalid URI would be (latitude "beyond" north pole). 9.2. Location Privacy Location information about individuals is an extremely sensitive topic, especially when location is combined with Personally Identifyable Information (PII). Authors of 'geo' URIs MUST consider data protection and privacy before publishing such URIs. 10. Acknowledgements The authors wish to acknowledge the helpful contributions from Carl Reed, Bill McQuillan, Martin Kofal, Andrew Turner and Kim Sanders. 11. References 11.1. Normative References [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. 11.2. Informative References [RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and Registration Procedures for New URI Schemes", BCP 115, RFC 4395, February 2006. [WGS84] National Imagery and Mapping Agency, "Department of Defense World Geodetic System 1984, Third Edition", NIMA TR8350.2, January 2000. Mayrhofer & Spanring Expires August 16, 2009 [Page 13] Internet-Draft 'geo' URI scheme February 2009 Authors' Addresses Alexander Mayrhofer nic.at GmbH Karlsplatz 1/9 Wien A-1010 Austria Phone: +43 1 5056416 34 Email: alexander.mayrhofer@nic.at URI: http://www.nic.at/ Christian Spanring OIR-ID GmbH Franz-Josefs-Kai 27 Wien A-1010 Phone: +43 1 5338747 36 Email: spanring@oir.at URI: http://www.oir.at/ Mayrhofer & Spanring Expires August 16, 2009 [Page 14]