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Dublin Core™ Metadata Initiative - DCMI Point Encoding Scheme

DCMI Point Encoding Scheme: a point location in space, and methods for encoding this in a text string

Creator: Simon Cox
Contributor: Andy Powell
Contributor: Andrew Wilson
Date Issued: 2006-02-13
Identifier: http://dublincore.org/specifications/dublin-core/dcmi-point/2006-02-13/
Replaces: http://dublincore.org/specifications/dublin-core/dcmi-point/2005-07-25/
Is Replaced By: http://dublincore.org/specifications/dublin-core/dcmi-point/2006-04-10/
Latest version: http://dublincore.org/specifications/dublin-core/dcmi-point/
Status of document: This is a DCMI Proposed Recommendation.
Description of document: This document defines DCMI Point, a mechanism for indicating a point in space using its geographic coordinates and representing that information as a value string. Components of the value string correspond to the location coordinates in north and east directions, plus optionally elevation, and also allow the coordinate system and units to be specified, and a name if desired. A method for encoding DCMI Point in a text string using the DCSV syntax is described. This notation is intended for representing a value of the DCMES element Coverage, particularly when using HTML meta elements.
Revision note: 2006-02-13. After approval of the DCMI Abstract Model [DAM] as a DCMI Recommendation in March 2005, the DCMI Usage Board undertook a review of the DCSV syntax specification and of the related specifications for the encoding schemes DCMI Box, DCMI Point, and DCMI Period, with the goal of revising their language for conformance with the Abstract Model. A summary of the changes made can be found in the document "Revision of legacy DCSV specifications". As of 1995, the DCMI Abstract Model supports the representation of complex structures, such as those encoded in DCSV-syntax-based encoding schemes, as "related descriptions". The DCMI Usage Board encourages implementers to consider the longer-term consequences for interoperability of packaging structured information in parsable DCSV-encoded string values as opposed to conveying that information in related descriptions using other syntax encodings.

Table of Contents

    1. Introduction
    1. Identifying a place - the DCMI Point scheme
    1. Encoding DCMI Point with DCSV Syntax
    1. Examples
    1. References

1. Introduction

Several methods are available generally to indicate a_place_. These include, but are not limited to:

  • a name , normally defined in an identifiable enumeration such as a gazetteer or list of jurisdictional localities;
  • a unique geocode , such as a postal code;
  • the coordinates of a point , using geographic values or some well-defined projection and units;
  • a set of arcs or faces describing the polygon or polyhedron comprising the perimeter of the place;
  • the limits of a regular shaped container which encompasses the place, typically a rectangular box in two or three dimensions, using geographic values or some well-defined projection and units.

The Dublin Core™ Metadata Element Set [DCMES] includes an element, Coverage , the value of which may be a place. If a name or geocode is used as the value representation for the property, then the enumeration from which that value is selected determines valid value strings. However, there are no simple, commonly used, notations for indicating a point using coordinates. Here we define DCMI Point, an encoding scheme which specifies the coordinates of the point location of a place, and describe a method for encoding DCMI Point in a text string using the DCSV syntax [DCSV]. If an identifier corresponding to an extensive region is required, then DCMI Box [BOX] is available for rectangular regions.

2. Identifying a place - the DCMI Point scheme

The place is indicated using a point location, described using coordinates in an identified cartesian system. The point may correspond to some place within an extensive region, such as the areal or volumetric centroid, but we do not specify the nature of the relationship in this document, nor is such specification necessary in a DCMI resource description.

We define the following components to describe the point:

Component Label Definition Default Component Value1
east The coordinate of the location measured in the east direction2 +/- INF3
north The coordinate of the location measured in the north direction2 +/- INF3
elevation The coordinate of the location measured in the vertical direction2 +/- INF3
units The units applying to unlabelled numeric values of north, east signed decimal degrees
zunits The units applying to unlabelled numeric values of elevation metres
projection The name of the projection used with any parameters required, such as ellipsoid parameters, datum, standard parallels and meridians, zone, etc geographic coordinates on Earth for north, east; height above mean-sea-level for elevation.
name A name for the place4 -

1 All components are optional.
2 Representations of component values are text strings representing numbers. Units should be included using conventional (SI) notation, unless the relevant units or zunits component is present. However, if units are given as part of any value component, then for this component these override those given by units or zunits.
3 If this component is absent then the value representation is undefined. Processors performing numeric comparisons are recommended to set value representations corresponding to maximally inclusive matching, i.e. the location is a line if one coordinate is missing, and a plane if two are missing.
4 In this context the name is non-normative. In the case of a conflict, the place identified by the coordinate values takes precedence. The name is provided for user convenience only.

3. Encoding DCMI Point

The components specified above have no meaning when disaggregated, since in any particular instance it is the complete set which acts to indicate a specific place. For systems in which data is encoded using a limited character set, this is conveniently accomplished by packaging the components into a single text string according to the DCSV syntax [DCSV].

A DCMI Point value string using DCSV syntax, and using the component names defined above appears as follows:

east=v1; north=v2; elevation=v3; units=v4; zunits=v5; projection=v6; name=v7

where v1 - v7 are component values as defined in the table above.

All components are optional but must not be repeated, and the ordering is not significant.

4. Examples

Perth, Western Australia:

name=Perth, W.A.; east=115.85717; north=-31.95301

Bridgnorth, Shropshire, U.K.:

east=372000; north=293000; units=m; projection=U.K. National Grid

The Greenwich Meridian:

east=0;

The highest point in Australia, illustrating the use of 3-D coordinates (and how flat Australia is):

east=148.26218; north=-36.45746; elevation=2228; name=Mt. Kosciusko

5. References

[BOX]
S. Cox, 2000. DCMI Box Encoding Scheme- specification of the spatial limits of a place, and methods for encoding this in a text string
http://dublincore.org/specifications/dublin-core/dcmi-box/

[DCMES]
1999. Dublin Core™ Metadata Element Set, Version 1.1: Reference Description
http://dublincore.org/specifications/dublin-core/dces/

[DCSV]
S. Cox, R. Iannella, 2000. A syntax for writing a list of labelled values in a text string
http://dublincore.org/specifications/dublin-core/dcmi-dcsv/