© ISO 2004 – All rights reserved
ISO TC 211/SC N
Date: 2004-08-16
ISO/WD 6709
ISO TC 211/SC /WG 9
Secretariat: NSF
Standard Representation of Geographic Point Location by Coordinates
Élément introductif — Élément central — Élément complémentaire
Warning
This document is not an ISO International Standard. It is distributed for review and comment. It is subject to
change without notice and may not be referred to as an International Standard.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of
which they are aware and to provide supporting documentation.
Document type: International Standard
Document subtype:
Document stage: (20) Preparatory
Document language: E
D:\106764007.doc STD Version 2.1c2
ISO/WD 6709
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ii
© ISO 2004 – All rights reserved
ISO/WD 6709
Contents
Page
Foreword ............................................................................................................................................................ iv
Introduction ......................................................................................................................................................... v
1
Scope ...................................................................................................................................................... 1
2
Conformance ......................................................................................................................................... 1
3
Normative references ............................................................................................................................ 1
4
Terms and definitions ........................................................................................................................... 2
5
Symbols and abbreviated terms .......................................................................................................... 3
6
UML Notation ......................................................................................................................................... 3
7
7.1
7.2
Requirements for the representation of point position ..................................................................... 3
Association to a coordinate reference syste ...................................................................................... 3
Textual representation .......................................................................................................................... 5
8
Representation by compound unit ...................................................................................................... 5
9
Requirements for the standard representation of latitude, longitude and height through
XML ......................................................................................................................................................... 5
Annex A (informative) The representation of degrees at the human interface or in geodetic
registers.................................................................................................................................................. 6
A.1
The representation of degrees at the human interface ..................................................................... 6
Annex B (informative) Latitude and longitude resolution ............................................................................... 7
Annex C (informative) Latitude and longitude coordinates are not unique .................................................. 8
Annex D (informative) XML Examples ............................................................................................................. 9
© ISO 2004 – All rights reserved
iii
ISO/WD 6709
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 6709 was prepared by Technical Committee ISO/TC 211, Geographic Information, Subcommittee SC , .
This second/third/... edition cancels and replaces the first/second/... edition (ISO 6709:1983), [clause(s) /
subclause(s) / table(s) / figure(s) / annex(es)] of which [has / have] been technically revised.
iv
© ISO 2004 – All rights reserved
ISO/WD 6709
Introduction
Efficient interchange of geographic point location data requires formats which are universally interpretable and
which allow unique identification of points on, above and below the earth’s surface. Users in various
disciplines may have different requirements. This is exemplified by the use of degrees and decimal degrees
as well as the traditional degrees, minutes and seconds for recording latitude and longitude. Users may also
require different degrees of precision and may use latitude and longitude without height.
This International Standard provides a variable-length format which has the flexibility to cover these various
requirements.
The first edition of this International Standard (ISO 6709:1983) provided for the representation of latitude and
longitude for geographic point locations. This second edition extends use of the representation to applications
requiring latitude or longitude values to be quoted separately, for example when quoting a difference in two
meridian values. It also extends the the representation of latitude and longitude to allow the values for each to
be held in separate numeric fields [whilst retaining the earlier text representation]. [Insert the text within []
only if we re-insert the 6709:1983 text string provisions]
This edition of the International Standard additionally provides for representation of horizontal point location by
coordinates other than latitude and longitude.
This edition also includes provisions for depths.
This International Standard is primarily intended for data exchange between computer systems. An
informative annex summarising the different requirements at the human interface has been added.
Use of this International Standard will:
a) reduce the cost of interchange of data;
b) reduce the delay in converting non-standard coding structures in preparation for interchange by
providing advance knowledge of the standard interchange format.
© ISO 2004 – All rights reserved
v
WORKING DRAFT
ISO/WD 6709
Standard Representation of Geographic Point Location by
Coordinates
1
Scope
This International Standard is applicable to coordinate interchange. It specifies the representation of
coordinates including latitude and longitude to be used in data interchange. It additionally specifies
representation of horizontal point location using coordinate types other than latitude and longitude. It also
specifies the representation of altitude, height and depth that may be associated with horizontal coordinates.
Representation includes unit representation and coordinate order.
This International Standard is not applicable to the representation of information held within computer
memories during processing, in their use in registers of geodetic parameters or in their potrayal at the human
interface. Informative annexes are included with recommendations for latitude and longitude in registers and
in portrayal.
This International Standard supports point position representation through XML. [For backward compatibility
with the first version it also allows for representation latitude, longitude and height or depth through a text
string.] [Insert the text within [] only if we re-insert the 6709:1983 text string provisions]
For latitude and longitude, this International Standard allows the use of normal sexagesimal notations
involving degrees, minutes and seconds as well as various combinations of sexagesimal and decimal
notations – degrees and decimal degrees; degrees, minutes and decimal minutes; degrees, minutes, seconds
decimal seconds.
This International Standard does not specify the use of fixed-length field formats which, although they may be
consistent with the format in this International Standard, require prior agreement between parties in the data
exchange.
This International Standard does not require special internal procedures, file organisation techniques, storage
medium, languages, etc., to be used in its implementation.
2
Conformance
To be described.
3
Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 1000 – SI units and recommendations for the use of their multiples and of certain other units
ISO 19111 – Geographic Information – Spatial referencing by coordinates
ISO 19115 – Geographic Information – Metadata
© ISO 2004 – All rights reserved
1
ISO/WD 6709
ISO TS 19127 – Geographic Information – Geodetic codes and parameters
ISO 19136 – Geographic Information – Geography Markup Language (GML)
4
Terms and definitions
For the purposes of this document, the following terms and definitions apply.
4.1
altitude
height where the chosen reference surface is mean sea level
NOTE
This definition is different from that in ISO 19116. PT discussed this from various viewpoints, such as safety
issues, and recommends this new. A submission to 19140 will be needed.
4.2
coordinate set
dataset of coordinate tuples related to the same coordinate reference system
4.3
coordinate tuple
tuple composed of coordinates
NOTE
the number of coordinates in the coordinate tuple shall equal the dimension of the coordinate system; the order
of coordinates in the coordinate tuple shall be identical to the order of the axes of the coordinate system
[ISO 19136 but with note added]
4.4
depth
distance of a point from a chosen reference surface measured downward along a line perpendicular to that
surface
4.5
height
h or H
distance of a point from a chosen reference surface measured upward along a line perpendicular to that
surface
NOTE
a height below the reference surface will have a negative value.
[Note to TMG: adapted from ISO 19111 which we believe should be replaced by this definition. In connection
with an NWIP 19111 revision and ISO 19116, a submission of this issue to 19140 and TMG will be needed.]
[Note to PT: above resulted from deletion of altitude from title. May not be needed.]
4.6
sexagesimal degree
plane angle represented by a sequence of values in degrees, minutes and seconds
NOTE
in the case of latitude or longitude, may also include a character indicating hemisphere.
NOTE
seconds'.
may require further discussion of the term `degree' in `sexagesimal degree' and `degrees, minutes and
2
© ISO 2004 – All rights reserved
ISO/WD 6709
4.7
tuple
ordered list of values [ISO 19136]
5
Symbols and abbreviated terms
Symbols
Not needed
Abbreviated terms
CRS
6
Coordinate Reference System
UML Notation
[Only required if UML diagram in clause 7 below is included in this doc. Not required if that diagram is
moved to 19111]
7
7.1
Requirements for the representation of point position
Association to a coordinate reference syste
Coordinates are numbers. A coordinate tuple represents position. ISO 19111 identifies several types of
coordinate tuple. A coordinate set is a collection of coordinate tuples. By definition, all coordinate tuples within
a coordinate set are referenced to the same coordinate reference system (CRS). Conversely, if coordinate
tuples have different CRSs they must be segregated into different coordinate sets. A coordinate tuple
represents position unambiguously only if the system to which it is referenced is defined. However for some
interchange purposes it is sufficient to confirm the identity of the system without necessarily having the full
system definition.
© ISO 2004 – All rights reserved
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ISO/WD 6709
<<Abstract>>
RS_ReferenceSystem (from ISO19111)
metadata?
0..1
+tupleCRS
name
0..1
<<Type>>
CoordinateSet
+setCRS
+set
+ encode(format : CharacterString) 0..*
+ decode(coordinateSet)
setCRS takes precedence
on tupleCRS when a
CoordinateTuple
in included in a CoordinateSet
1..*
<<Type>>
CoordinateTuple
+ coordinate [1..*] : real
+
+
+
+
+
+tuple
encode()
1..*
decode(aCoordinateTuple)
directPosition() : DirectPosition
GM_Point() : GM_Point
GM_Position() : GM_Position
[Should this be moved to 19111 revision ?]
.A coordinate reference system (CRS) identification or definition in accordance with ISO 19111 shall be
associated with every coordinate tuple. It is not necessary to supply the CRS definition with every point; if a
CRS is associated with a coordinate set, all coordinate tuples in that coordinate set inherit the association.
One CRS identification or definition shall be associated with each coordinate set.
The CRS identification shall be through:
either
(a) reference to a definition in a register of geodetic parameters conforming to the requirements
of ISO TS 19127.
or
(b) a full coordinate reference system definition as defined in ISO 19111.
(a) and (b) are alternative means of providing a full CRS definition. (a) is recommended for simplicity but if the
system definition is not available from a register it shall be given in full. In both methods the order of
coordinates in each coordinate tuple shall be as given in the CRS definition.
When using method (a), reference to a geodetic register, applications that require only to confirm the
identification of a CRS can do so through the register citation and CRS unique identifier from that register.
They do not need to retrieve the elements that constitute the CRS definition from the register unless there is a
need to quote these or to perform a coordinate operation on the coordinate set.
The syntax required for the CRS definition by geodetic register in (a) above is:
(i) for an online register:
crsName=”url”
for example: crsName=”http://www.epsg.org#epsg:4326”
or
4
(ii) for a register which is not online:
© ISO 2004 – All rights reserved
ISO/WD 6709
crsName=[registerID]:[register’s CRS ID]
for example: crsName=epsg:4326
[Need to confirm syntax and ensure it is consistent with 19127.]
7.2
Textual representation
NOTE
The original textual representation of ISO 6709:1983 is intentionally excluded in this Working Draft to ask
Member Bodies to check again whether such representation is practically used in some application fields and what type of
textual representation is appropriate from the viewpoint of ISO/TC211.
8
Representation by compound unit
A unit has a fixed ratio to an SI base unit (radian, metre). For example one degree equals /180 radians [ISO
1000]. A degree may sometimes be represented as a compound structure consisting of other smaller units
(minutes or minutes and seconds). For example
12°35'24" is equivalent to 12.59 degrees.
9 Requirements for the standard representation of latitude, longitude and height
through XML
Latitudes on or north of the equator shall be positive, latitudes south of the equator shall be negative.
Longitudes on or east of the prime meridian shall be positive, longitudes west of the prime meridian shall be
negative. The 180th meridian shall be negative. The prime meridian is usually Greenwich; this is identified
through the coordinate reference system definition.
For digital data interchange latitude and longitude shall each be in degrees
[we need to decide on only one of these two options:(a) represented as a decimal number in degrees.
(b) in the representation given in the coordinate reference system defintion
The syntax required for describing values in a coordinate tuple is
[need to describe XML elements - see example]
Examples are given in Annex D.
© ISO 2004 – All rights reserved
5
ISO/WD 6709
Annex A
(informative)
The representation of degrees at the human interface or in geodetic
registers
A.1 The representation of degrees at the human interface
It should not be assumed that decimal degrees are required at the human interface. Each user community has
its own requirements for notations involving degrees, minutes and seconds as well as various combinations of
sexagesimal and decimal notations – degrees and decimal degrees; degrees, minutes and decimal minutes;
degrees, minutes, seconds decimal seconds.
The order of coordinates may be critical. Historical conventional usage gives latitude value before longitude
value. Users in the marine and air navigation fields and involved with emergency response are used to seeing
latitude and longitude given in this order. If height or depth is also given it will follow longitude. To present
coordinate values in another order have safety of life implications.
Coordinate values can most easily be understood when well laid out. User communities will have their specific
requirements for representation. In the absence of a user community specification is recommended that:
-
each coordinate in a coordinate tuple is separated by a space;
-
each coordinate tuple is on a separate line of display;
-
degree, minute and second units are identified with symbols
-
the recommended symbols are ° ' and " (ASCII codes 176, 39 and 34) respectively
-
the symbols should follow their value
-
there should be no spaces should between degree, minute, second and hemisphere values.
-
latitude hemisphere is indicated through the first letter of the hemisphere (N or S, ASCII codes 78
and 83 respectively);
-
longitude hemisphere is indicated through the first letter of the hemisphere (E or W, ASCII codes
69 and 87 respectively);
-
the separator for integer and fractional parts of a value will normally be set in the user’s operating
system;
-
the integer part of height or depth values should include a 103 separator. The separator used will
normally be set in the user’s operating system.
For example:
50°40'46.461"N
95°48'26.533"E 1,123.45m
50°03'46.461"N 125°48'26.533"E
6
978.90m
© ISO 2004 – All rights reserved
ISO/WD 6709
Annex B
(informative)
Latitude and longitude resolution
It is recommended that coordinates are quoted to a resolution communsurate with their accuracy. The
resolution of coordinates is only a recommended indicaton of their accuracy. The accuracy of coordinates or
of a position shall be given according to xxx. [cross reference to appropriate clause or IS]
For the Earth, at the equator 1 degree of latitude and longitude are each equivalent to approximately 110
kilometres; 1 minute equivalent to approximately 1 mile and 1 second equivalent to approximately 30 metres.
The table below gives recommended resolution to which latitude and longitude should be given for various
accuracies.
Accuracy
Recommended Resolution
Decimal degrees
100 km
1 km
10 m
Sexagesimal degrees
1
1 deg
0.01
1 min
0.001
1 sec
1m
0.00001
1 cm
0.0000001
© ISO 2004 – All rights reserved
0.1 sec
0.001 sec
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ISO/WD 6709
Annex C
(informative)
Latitude and longitude coordinates are not unique
Latitude and longitude are measurements on a model of the Earth, normally an ellipsoid. Several hundred
models have been defined and about forty different models remain in daily use. The selection of model
together with its position and orientation relative to the Earth is defined through a geodetic datum. If the
model or its position or orientation is changed, that is if the geodetic datum is changed, the values of latitude
and longitude at a point will usually change. The same values of latitude and longitude referenced to different
datums will refer to different locations (see Figure D.1). Conversely, for coordinate values to be unambiguous
the datum to which they are referenced must be identified.
Figure C.1 — Locations with identical latitude and longitude values on three different coordinates
OSGB 1936
x
x
x
WGS 84
ED50
100 metres
“WGS 84”, “ED50” and “OSGB 1936” are the identifiers of some geographical coordinate reference systems.
Projected coordinates are derived from geographic (latitude and longitude) coordinates. Hence for the
projected coordinates to be unambiguous the datum for their source geographic coordinates must also be
identified.
The differences in coordinate values of a point caused by change of geodetic datum are typically about 50 to
500 metres but can be considerably more in extreme cases. When dealing with coordinates with an accuracy
of 1 kilometre or worse, or mapping at scales of 1:1,000,000, 1:2,000,000 or smaller, these differences are not
significant. But for applications requiring an accuracy of better than 1 kilometre, or mapping at scales of larger
than 1:1,000,000, if coordinates are to be unambiguous the identification of their datum is essential.
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© ISO 2004 – All rights reserved
ISO/WD 6709
Annex D
(informative)
XML Examples
EXAMPLE 1
Degrees, minutes and decimal seconds (DD MM SS.SS) with the CRS identification from an online
geodetic register
<point crsName="http://www.epsg.org#epsg:4326">
<coordinateTuple>
<latitude>
<dmsAngle>
<degrees>
50
</degrees>
<minutes>
25
</minutes>
<decimalSeconds>
12.059
</decimalSeconds>
</dmsAngle>
</latitude>
<longitude>
<dmsAngle>
<degrees>
12
</degrees>
<minutes>
35
</minutes>
< decimalSeconds >
24.478
</ decimalSeconds >
</dmsAngle>
</longitude>
</coordinateTuple>
</point>
EXAMPLE 2
Degrees and decimal minutes (DD MM.MM)
<point crsName="http://www.epsg.org#epsg:xxxx">
<coordinateTuple>
<latitude>
<dmsAngle>
<degrees>
50
</degrees>
<decimalMinutes>
25.2
</decimalMinutes>
</dmsAngle>
</latitude>
<longitude>
<dmsAngle>
<degrees>
12
</degrees>
<decimalMinutes>
35.4
</decimalMinutes>
</dmsAngle>
© ISO 2004 – All rights reserved
9
ISO/WD 6709
</longitude>
</coordinateTuple>
</point>
EXAMPLE 3
Decimal degrees (DD.DD) and depth from an offline geodetic register
<point crsName=epsg:xxxx>
<coordinateTuple>
<latitude>
<dmsAngle>
<decimalDegrees>
50.42
</decimalDegrees>
</dmsAngle>
</latitude>
<longitude>
<dmsAngle>
<decimalDegrees>
-22.59
</decimalDegrees>
</dmsAngle>
</longitude>
<depth>
543.43
</depth>
</coordinateTuple>
</point>
EXAMPLE 4
Grid coordinates
<point crsName="http://www.epsg.org#epsg:21418">
<coordinateTuple>
<northing>
1259753
</northing>
<easting>
18503245
</easting>
</coordinateTuple>
</point>
EXAMPLE 5
Grid coordinates with height
<point crsName="http://www.epsg.org#epsg:xxxx">
<coordinateTuple>
<easting>
503245.81
</easting>
<northing>
125906.56
</northing>
<height>
43.43
</height>
</coordinateTuple>
</point>
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© ISO 2004 – All rights reserved