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==Thoughts on extending the geo microformat==
'''This page and effort is failing to follow the microformats [[process]]. If you are the author of this page, please join the [http://microformats.org/discuss #microformats IRC channel and/or microformats-discuss mailing list] so that the community can help walk you through the process.''' - Tantek
 
==4d: A geo microformat alternative proposal==


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; Editor/Author: [[User:DimitriosZachariadis|DimitriosZachariadis]] 17:03, 23 Jan 2007 (PST)
The term ''4d'' stands for ''four dimensions'' and is used interchangeably with ''spacetime'' in this page, as heaving the same meaning. When in bold, it means the proposed microformat '''4d'''.


; Editor/Author: [[User:DimitriosZachariadis|DimitriosZachariadis]] 17:03, 17 Jan 2007 (PST)
<div style="color:red;">Page under construction</div>
__toc__
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===Abstract===
A compact microformat for defining locations and events is proposed, as an alternative for the draft '''geo''' microformat. A tolerant five part, semicolon separated, spacetime and reference-system value, is argued to be sufficient to provide accurate information for uniquely identifying a place or an event in a four dimensional universe.
<div>&nbsp;</div>


===Introduction===
===Introduction===
The need for inclusion of altitude, time and reference system in the geo microformat is discussed. A five part value, semicolon separated, is argued to be sufficient for uniquely identifying a place or an event in a four dimensional universe.


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'''<span style="font-size:2em">L</span>'''OCATION and geo referencing microformats proposed on this site, namely [[geo]], [[luna]] and [[mars]] have at present a status of draft. With this in mind, a number of issues regarding the need for time and a reference system are presented for discussion.
'''<span style="font-size:2em">L</span>'''OCATION and geo referencing microformats proposed on this site, namely [[geo]], [[luna]] and [[mars]] have at present (Jan 2007) a status of draft. Dealing with the issue of geo tagging requires a consensus on the issues of importance, if the microformat is to be successful and used without problems. To that extend, a proposal for a new microformat might not be superfluous, if it can present and offer for discussion some of the issues at hand. With that ambition, the '''4d''' microformat is presented and discussed herein.
 
===Brief discussion===
 
Most of the location related information, whether about the Earth or another celestial body, have a time related aspect attached; historical places and events, geographical features, but also street names and addresses are tightly related to an act or an observation made at some point in time; addresses used today may have not been in use a century ago (assuming the place identified by the coordinates did exist), or may well change to something different tomorrow. Landmarks existing for centuries have an age, which means they have a birthday, but they may also one day disappear.
 
A vast amount of information used by people on a daily basis in the web is in fact an aggregation of events; stories and descriptions are most of the time nothing more than annotations of events. As such, most of this information can be accurately tagged, stored and used for as long as it exists, if its spacetime dimensions are known.  
 
===Default values and ambiguities===


===Time===
Disambiguation of the values used for tagging is an important issue, if the data tagged are to be valid, accurate and and useful outside the assumptions made at the time of their creation.
In a four dimensional space, a point represents an event; three dimensional geometry, cartography, and time, can all be thought of as subsets of spacetime; a location on a map is expressed in a 2D spacetime subset, a photograph in a 3D subset where time is the 3rd dimension.
Omitting dimensions from a 4d coordinate system introduces assumptions about their default values. To demonstrate the issues that need to be dealt with, the following example of a markup, tagged with the geo microformat, might prove useful:


It can be argued, that most of the location related information, whether on Earth or on another celestial body, have a time related aspect attached; historical places and events, geographical features, are usually related to an act or an observation made at some point in time. Landmarks existing for centuries have an age, which means they have a birthday, and most probably a death. Photographs and videos can be thought as 3D snapshots (2D+time) in a 4D continuum.
<pre><nowiki>
In 1687, a Turkish ammunition dump


A large amount of location information used by people on a daily basis on the web, is in fact an aggregation of events; stories, news, photographs and videos, even items auctioned on ebay are nothing more than snapshots of spacetime. As such, most of this information can be accurately tagged, stored and used for as long as it exists, if its spacetime dimensions are known.
<a class="geo" href="http://maps.google.com/maps?q=37.971508,23.72658&ie=UTF8&z=18&ll=37.971508,23.72658
&spn=0.002584,0.006083&t=k&om=1&iwloc=addr">
inside the building
<abbr class="latitude" title="37.971508"></abbr>,  
<abbr class="longitude" title="23.72658"></abbr>
</a>


It is obvious that the inclusion of a time dimension in the geo markup moves the focus of geo tagging from the realm of two dimensional cartography to the realm of events; events are about stories, cartography is about navigation. People are interested in stories, news and events, which undoubtedly constitutes most of the information viewed with a web browser; few people can successfully navigate a car using a map and even fewer are interested in navigation and cartography as a science or art. Geographic coordinates shown in texts are quite useless without a map. Humans use names to identify places, not numbers. The reason geographic coordinates exist in text, is merely to help humans manually identify places on maps. If things can be done electronically, then numbers don't seem to matter a lot any more.
was ignited by a Venetian cannonball. The resulting explosion severely damaged
the Parthenon and its sculptures.
</nowiki></pre>


=====Real world examples=====
which may be rendered as:
Countless examples of 2D+time events exist:


*[http://flickr.com/map/ flickr]: geotagged photos with a date of capture.
''In 1687, a Turkish ammunition dump [http://maps.google.com/maps?q=37.971508,23.72658&ie=UTF8&z=18&ll=37.971508,23.72658&spn=0.002584,0.006083&t=k&om=1&iwloc=addr inside the building]'' <span class="geo"><abbr class="latitude" title="37.971508"></abbr><abbr class="longitude" title="23.72658"></abbr></span>
*[http://www.youtube.com/categories_portal?c=19&e=1 youtube]: videos with a location and a date.
''was ignited by a Venetian cannonball. The resulting explosion severely damaged the Parthenon and its sculptures.'' [http://en.wikipedia.org/wiki/Parthenon Wikipedia, The Parthenon]
*[http://en.wikipedia.org/wiki/Main_Page wikipedia, In the news]:  front page news, "On this day..."
*[http://www.bbc.co.uk/ BBC]: news
*[http://www.nasa.gov/externalflash/Mars_as_art/index_noaccess.html Mars As Art]
*[http://www.nasa.gov/mission_pages/mars/main/index.html NASA: Explore Mars]: space exploration vehicles, celestial body features, [http://www.nasa.gov/missions/past/index.html Missions]
*[http://ciclops.org/index.php Cassini imaging]


Examples of loose, or changing, attachment of time to location also exist:
In the case of the markup above, a human reader would ''assume'' that the coordinates involved in the code have been taken using WGS86, the most known and used datum ''today'', due to its global validity and the proliferation of the GPS receivers. The ambiguity of altitude leads to an assumption of a default value of 0, which is acceptable for 2D cartography. No assumption can be made about time.


An example from [http://www.ebay.com/ ebay] is indicative:
===Verbosity===
If the geo portion of the above markup is reduced to:
<pre><nowiki>
<pre><nowiki>
End time: Jan-29-07 06:18:15 PST (6 days 21 hours)
<a class="geo" href="http://maps.google.com/maps?q=37.971508,23.72658&ie=UTF8&z=18&ll=37.971508,23.72658
Shipping costs: US $1.88
&spn=0.002584,0.006083&t=k&om=1&iwloc=addr">
                US Postal Service First Class Mail®
inside the building
                Service to United States
<abbr class="latitude" title="37.971508"></abbr>,  
                (more services)
</a>
Ships to: Worldwide
Item location: Dinwiddie, Virginia, United States
History: 0 bids
</nowiki></pre>
</nowiki></pre>


===Different times===
the markup becomes useless for identifying locations, since it no more represents a location (but rather a geometric ''locus''). If this is the case, then it seems that there is no point in having latitude and longitude defined by separate tags; indeed, the meaning of a coordinate is that it is an ordered list of numbers, or a tuple. [http://en.wikipedia.org/wiki/Coordinates Wikipedia, Coordinates]. RFC2426[2] also specifies the GEO type as a single ''lat;long'' entity.
Dealing with time in multiple reference systems is not quite the same as dealing with local time. It might not be necessary for humans to do it in their daily life, but it is important when when information on a global, or universal basis is involved. Different cultures, use different reference systems to tell the time. [http://en.wikipedia.org/wiki/Islamic_calendar Islamic calendar],[http://en.wikipedia.org/wiki/Hebrew_calendar Hebrew calendar], [http://en.wikipedia.org/wiki/Egyptian_calendar Egyptian calendar].


In a similar manner, trying to understand Martian time, while living on Earth, involves more than a simple addition/subtraction of a few hours. A Martian day, is not of the same duration as a Terran day, and the same is true for the duration of the seasons; a human cannot get a "7 hours behind local time" sync with Martian time; a number of connotations, that would otherwise help in getting a gut feeling, fail helplessly.
It could be argued that having a simpler, albeit verbose, format, helps content formating tools like XSLT processors, locate data easier. However, ''Microformats are a way of adding simple markup to human-readable data items such as events, contact details or locations, on web pages, so that the information in them can be extracted by software and indexed, searched for, saved, cross-referenced or combined''. Microformats are not meant to help format content for humans, but to help machines gather information in a Semantic Web. On the other hand, a machine can split the data of a '''4d''' tag in one single line of code.
 
===Time===
As argued above, the inclusion of a time dimension in geo markup can add significantly to the semantics of a piece of geo information, as it moves the focus of geo tagging from the realm of two dimensional cartography to the realm of events.


Different calendars and time standards should have a place in the Semantic Web.  
This should come as no surprise: events are about stories; cartography is about navigation. People are interested in stories, news and events; few people can successfully navigate using a map and even fewer are interested in navigation and cartography as a science or art. Geographic coordinates shown in the text are quite useless without a map, and are even more useless if an electronic map is available for use. Humans use names to identify places, not numbers. The reason there is a need for showing geographic coordinates in text, is mostly to help humans manually identify places on maps. If this can be done electronically, then numbers don't seem to matter.
 
A human visiting the page with the markup above (which was chosen for the length of the time dimension and the connotations involved), will have a chance to read the text (and the year of the event, which however is un-tagged), click at the link and get a Google Map centered at the Acropolis and the Parthenon. Semantic connotations for humans enhance their understanding of information presented to them.[1] However, a machine seeking information in the Semantic Web, will have no way of finding out if it is the 5th century BC Athenian state or the contemporary Greek state that this particular piece of information is referring to. Semantic information about that particular markup that could otherwise be cataloged by the machine, will pass unnoticed.
 
Had this geo markup been amended with a time dimension, a robot crawling this and other similar pages could create a list of historical events, based on nothing else but the information provided by the '''4d''' microformat.
 
Humans have learned to deal with time efficiently, in their locality, through the use of clocks. Wrist watches remind people of upcoming events in their lives. An event in a remote place is more difficult to conceive, but not entirely impossible. Although it involves a simple addition or subtraction, only people traveling a lot can do it with ease.
 
Counting time in multiple reference systems is however a difficult task. It might not be necessary for humans in their daily life, but it is important when dealing with information on a global, or universal basis. Different cultures, use different reference systems to tell the time. [http://en.wikipedia.org/wiki/Islamic_calendar Islamic calendar] These need to be taken into account in a Semantic Web.
 
In a similar manner, trying to addapt to a Martian reference system, while living on Earth, involves more than a simple addition/subtraction of a few hours. A Martian day, is not of the same duration as a Terran day, and the same is true for the duration of the seasons; a number of connotations, that would otherwise help in getting a gut feeling, fail helplessly.


===The reference system===
===The reference system===
Although the geo microformat specification states WGS84 as the reference system used, this is not a trivial issue: Only 20 years ago, the same coordinates would possibly point hundreds of meters away from a location, since the reference system used at that time was different than WGS84. Furthermore, the same coordinates may not be accurate 10 years from today, when the WGS84 reference system will have been revised once again. Besides this, there is a number of other coordinate systems that are used extensively today, like the Universal Transverse Mercator (UTM) system, that are excluded from the geo specification. The problem is that tying a microformat specification to a particular reference system, and only that, may be a limiting factor for the microformat.
It should be noted that the assumption about the datum used in expressing the lat-long coordinates mentioned above, is not a trivial one: Only 20 years ago, the same coordinates would possibly point hundreds of meters away from the Parthenon, since the reference system used at that time was different than WGS84. Furthermore, assuming WGS84 was the datum for the markup above, these coordinates may not be accurate 10 years from today, when the WGS84 reference system will have been revised once again.


A markable indication of the importance of the reference system, when expressing geo coordinates, is the fact that the Greenwich Observatory, which was by definition the origin for the longitude coordinate for more than a century, lies now about 102.5m West of the WGS84 0.0 meridian, at N 51° 28' 36.71, W 0° 0' 5.18", (in WGS84 datum) according to [http://en.wikipedia.org/wiki/Prime_Meridian Wikipedia, Prime_Meridian]. Interestingly, Google maps and Wikipedia do not seem to agree on these coordinates ([http://maps.google.com/maps?f=q&hl=en&q=51.476864,-0.000518&ie=UTF8&z=19&ll=51.476861,-0.000515&spn=0.001067,0.002175&t=h&om=1&iwloc=addr map])
A markable indication of the importance of the reference system, when expressing geo coordinates, is the fact that the Greenwich Observatory, which was by definition the origin for the longitude coordinate for more than a century, lies now about 102.5m West of the WGS84 0.0 meridian, at N 51° 28' 36.71, W 0° 0' 5.18", (in WGS84 datum) according to [http://en.wikipedia.org/wiki/Prime_Meridian Wikipedia, Prime_Meridian]. Interestingly, Google maps and Wikipedia do not seem to agree on these coordinates [http://maps.google.com/maps?f=q&hl=en&q=51.476864,-0.000518&ie=UTF8&z=19&ll=51.476861,-0.000515&spn=0.001067,0.002175&t=h&om=1&iwloc=addr map]  
<span class="geo">
<span class="geo">
<abbr class="latitude" title="51.476864"></abbr>
<abbr class="latitude" title="51.476864"></abbr>
Line 69: Line 97:
</span>
</span>


When geo tagging information about other celestial bodies, the need for a reference system is even more pronounced; lacking familiar country or city names makes feature identification a difficult task. Existing reference systems are bound to change many times, as more data becomes available for these bodies.
It should be clear that, for a microformat to be able to convey accurate information, well defined and known reference systems should be used. By performing transformations among the various reference systems, the content referenced in one system can be understandable and usefull on another, on a global or universal basis.


For a microformat to be able to convey accurate information, well defined and known reference systems should be specified together with the data. Geo reference systems, such as WGS84, also make references to the time standard used [http://earth-info.nga.mil/GandG/publications/tr8350.2/wgs84fin.pdf WGS84 Definition]. Transformations among the various reference systems can make content referenced by geo data in one system understandable and usefull on another.
===Name convention===
Naming a geo microformat '''4d''' helps avoid the problem of the geo-centric (i.e. Earth bound) root of the word '''geo'''; '''4d''' can be easily used on any celestial body for which a reference system, even rudimentary, has been defined. To that extend, Mars related content can be readily ''microformatted'' and displayed on [http://www.google.com/mars Google Mars]. Obviously, matters regarding reference systems of other celestial bodies require expert knowledge, however, reading the news on NASA's site, e.g. for Titan, [http://www.nasa.gov/mission_pages/cassini/multimedia/pia09111.html Two Sides of Dunes], reveals that reference systems are in place for all celestial bodies visited by a man made spacecraft, and probably for a lot more than those.


==Thoughts on specification extension==
'''4d''' is a rather common acronym; Google yields about 53.9 million hits, while for '''3d''' it yields 310 million hits and for '''geo''' 82.9 million.
The geo microformat as it stands today, offers a representation of a point in a 2D space. Both expanded and compact forms of geo provide decimal number representations of coordinates suitable for machines.


===Expanded form===
==Specification==
The new properties to implement the additional dimensions of altitude and time could be:
It is proposed that the '''4d''' microformat be formed as follows:
* dtstamp, as found in hCalendar
* altitude, or the z direction
* georef


The dimension of time could be represented by reusing the ''dtstamp'' property found in [http://microformats.org/wiki/hcalendar hCalendar]. The calendar to be used, depends on the reference system, and for WGS84 is the Gregorian calendar.
===Root Class Name===
The root class name for a '''4d''' location/event is ''4d''


The dimension of altitude could be represented by the use of an ''altitude'' property, expressed in the WGS84 reference system in meters.
===Property List===
The '''4d''' microformat has the following no properties.


The ''georef'' property is a string determining the reference system, e.g. "WGS84". Additional fields could be allowed with the use of the delimiter ":", e.g. "MARS:J2000" (fictional).
===Value===
 
The value of a '''4d''' location/event resides in the ''title'' attribute of an (X)HTML tag as a semicolon separated 5-tuple:
===Compact form===
The value of an extended geo location/event resides in the ''title'' attribute of an (X)HTML element as a semicolon separated 5-tuple:
  ''v1;v2;z;t;u''  where:
  ''v1;v2;z;t;u''  where:
   
   
  ''v1'' is either latitude or x, depending on ''u''
  ''v1'' is either latitude or x, depending on ''u'', mandatory
  ''v2'' is either longitude or y, depending on ''u''
  ''v2'' is either longitude or y, depending on ''u'', mandatory
  ''z'' is the altitude
  ''z'' is the altitude, optional
  ''t'' is the time
  ''t'' is the time, optional
  ''u'' is the reference system code
  ''u'' is the reference system code, optional


The original form ''lat;lon'' is a valid form. To disambiguate this data, the reference system used in this case should have been specified globally for the page.
Dimensions ''z'', ''t'', and ''u'' can be omitted. If abiguities arrise from such an omition, e.g. omiting the ''z'' and ''t'' dimensions but defining the ''u'' dimension, then the relevant field values must be left empty, e.g.: ''v1;v2;;;u''
 
Dimensions ''z'', ''t'', and ''u'' can be omitted if they are at the end of the tuple. However, if omitting the ''z'' and ''t'' dimensions but defining the ''u'' dimension, then the relevant field values must be left empty, e.g.: ''v1;v2;;;u''.
 
Dimensions v1 and v2 could also theoretically be omitted, e.g. ''23.5'' may represent the tropic of Cancer, '';0.0'' the Greenwich Meridian, while '';;;2007'' expresses the time (assuming a WGS84 reference system), although the latter could be better represented by a ''dtstamp'' property. However, such representations are obscure and do not add to the clarity of the data.


===Default Reference System===
===Default Reference System===
The vCard, RCF2426 specification, which has been the basis for the geo microformat, does not specify a reference datum, but it specifies ISO-8601 as the standard for the UTC-OFFSET value type used in the TZ (timezone) type. hCalendar uses ISO-8601 (date)time formats.
The default reference system is WGS84 and the Gregorian calendar.


The reference system specified by the geo microformat is WGS84. WGS84 in turn uses UTC to count (date)time which is based on the Gregorian calendar. It should be possible for the reference system to be explicitly stated either globally or within the geo data tuple. Units for data in the geo microformat are those specified in the reference system used.
The time dimension is expressed in the ISO-8601 format ("YYYY-MM-DDThh:mm:ss.ssZ"), in any of its abbreviations and forms. [http://www.w3.org/TR/NOTE-datetime W3C, Date and Time Formats] and [http://en.wikipedia.org/wiki/ISO_8601 Wikipedia, ISO-8601]


===Meta data===
===Meta data===
The default reference system could be set, using the ''name'' and ''content'' attributes of the ''meta'' (X)HTML element, as follows:
The default reference system may be set, using the ''name'' and ''content'' attributes of the ''meta'' (X)HTML element, as follows:


  <meta name="georef" content="''reference-system''"/>
  <meta name="4d.reference" content="''reference-system''"/>


===Default coordinate values===
===Default coordinate values===
Only the ''z'' dimension (altitude, in WGS86) when omitted assumes a '''0.0''' meters value.
When a dimension is omitted, the following default values are implied:


The default reference system for an (X)HTML page should be set by using meta data properties, if the geo data tuple defines no reference system. The inclusion of the meta data element ensures the validity of the spacetime data for as long as the page exists, while keeping geo values compact. By adding the '''georef''' metadata property, a transition to the extended geo microformat would require no further change to the markup.
''u'': '''WGS84'''
''v1'': latitude, expressed in decimal degrees, no default
''v2'': longitude, expressed in decimal degrees, no default
''z'': altitude, expressed in meters, defaults to '''0.0'''
''t'': time, no default


===Significant digits===
The default reference system for an (X)HTML page can be set by using meta data properties.
A human reader interpretes the number of signifficant digits given in a number as a measure of the accuracy of the number. The number of significant digits in the coordinates could be related to the '''scale''' that a particular cartographic (or other) representation of a 4D point should be rendered in.


An application could use this expression accuracy, e.g. the number of decimal digits present in a coordinate to derive the '''zoom''' factor for a map showing the specific location.
<span style="color:#080;font-weight:bold;">It is strongly recommended that web pages include a meta data element that defines the default reference system, in their HTML head section</span>. The inclusion of the meta data element ensures the validity of the 4d data for as long as the page exists, while keeping '''4d''' values compact. By adding the '''4d''' metadata element, a conversion from the '''geo''' microformat to the '''4d'''   would only require the change of the root class, from ''geo'' to ''4d''.


===Reference systems===
===Reference systems===
Other reference systems include:
Indicative reference systems include:
* UTM:''zone''
* UTM:zone
** ''v1'' is ''x'', expressed in meters
** ''v1'' is ''x'', expressed in meters
** ''v2'' is ''y'', expressed in meters
** ''v2'' is ''y'', expressed in meters
** ''t'' is expressed in ISO-8601
** ''t'' is expressed in ISO-8601
** ''zone'' is the UTM zone
...more


==Examples==
==Examples==
The markup used in the discussion, transferred in the '''4d''' microformat:
<pre><nowiki>
In 1687, a Turkish ammunition dump
<a class="4d" href="http://maps.google.com/maps?q=37.971508,23.72658&ie=UTF8&z=18&ll=37.971508,23.72658
&spn=0.002584,0.006083&t=k&om=1&iwloc=addr">
inside the building
<abbr class="4d" title="37.971508;23.72658"></abbr>
</a>
was ignited by a Venetian cannonball. The resulting explosion severely damaged
the Parthenon and its sculptures.
</nowiki></pre>
====Example 1====
====Example 1====
Hidden 4D coordinates, no content
Hidden 4d coordinates, no content
<pre><nowiki>
<pre><nowiki>
The Parthenon was ruined by a Venetian cannonball in 1687
The Parthenon was ruined by a Venetian cannonball in 1687
<abbr class="geo" title="37.971508;23.72658;;1687">
<abbr class="4d" title="37.971508;23.72658;;1687"></abbr>
</nowiki></pre>
</nowiki></pre>


====Example 2====
====Example 2====
Hidden 2D coordinates and georef, free text content, expanded form
Hidden 4d coordinates, free text content
<pre><nowiki>
<pre><nowiki>
<span class="geo">
<span class="4d" title="37.971508;23.72658;;1687">
    The Parthenon was ruined by a Venetian cannonball in  
The Parthenon was ruined by a Venetian cannonball in 1687
    <abbr class="dtstamp" title="1687">1687</abbr>
    <abbr class="latitude" title="37.971508"></abbr>
    <abbr class="longitude" title="23.726580"></abbr>
    <abbr class="georef" title="WGS84"></abbr>
</span>
</span>
</nowiki></pre>
</nowiki></pre>
may be rendered as:
may be rendered as:


''<span class="geo">The Parthenon was ruined by a Venetian cannonball in <abbr class="dtstamp" title="1687">1687</abbr><abbr class="latitude" title="37.971508"></abbr><abbr class="longitude" title="23.726580"></abbr></span>''
''<span class="4d" title="37.971508;23.72658;;1687">The Parthenon was ruined by a Venetian cannonball in 1687</span>''
 
The same in compact form:
<pre><nowiki>
<span class="geo" title="37.971508;23.72658;;1687;WGS84">
The Parthenon was ruined by a Venetian cannonball in 1687
</span>
</nowiki></pre>


====Example 3====
====Example 3====
Visible 4d coordinates
Visible 4d coordinates
<pre><nowiki>
<pre><nowiki>
<abbr class="geo" title="37.971508;23.72658;;1687;WGS84">N 37° 58' 17.43, E 23° 43' 35.69</abbr>
<abbr class="4d" title="37.971508;23.72658;;1687">N 37° 58' 17.43, E 23° 43' 35.69</abbr>
</nowiki></pre>
</nowiki></pre>


may be rendered as:
may be rendered as:


''<abbr class="geo" title="37.971508;23.72658;;1687;WGS84">N 37° 58' 17.43, E 23° 43' 35.69</abbr>''
''<abbr class="4d" title="37.971508;23.72658;;1687">N 37° 58' 17.43, E 23° 43' 35.69</abbr>''


====Example 4====
====Example 4====
Minimal HTML page:
Minimum HTML page:


<pre><nowiki>
<pre><nowiki>
Line 182: Line 208:
   <head>
   <head>
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
     <meta name="georef" content="WGS84"/>
     <meta name="4d.reference" content="WGS86"/>
   </head>
   </head>
<body>
<body>
   <div class="geo" title="51.476864;-0.000518">
   <div class="4d" title="51.476864;-0.000518">
   The Greenwich Observatory
   The Greenwich Observatory
   </div>
   </div>
Line 193: Line 219:


====Example 5====
====Example 5====
A fictitious Mars reference system, using Mars coordinates from Google Mars:
A fictitious Mars reference system, using actual Mars coordinates from Google Mars:
<pre><nowiki>
<pre><nowiki>
<span class="geo" title="18.302380;-133.472900;;;MARS:J2000">
<span class="4d" title="18.302380;-133.472900;;;MARS:J2000">
Olympus Mons, Mars: The highest mountain in the solar system.
Olympus Mons, Mars: The highest mountain in the solar system.
</span>
</span>
Line 202: Line 228:
rendered as:
rendered as:


''<span class="geo" title="18.302380;-133.472900;;;MARS:J2000">Olympus Mons, Mars: The highest mountain in the solar system.</span>''
''<span class="4d" title="18.302380;-133.472900;;;MARS:J2000">Olympus Mons, Mars: The highest mountain in the solar system.</span>''


===Implementation example===
A page with the above examples and a minimal javascript helper, opening a Google map in a separate window, using the number of significant digits as a guide for the zoom:


Only for Firefox at the moment:
====Real world example====
[http:// A crafted page with the examples appering here and a small map demonstration]


[http://microformats.telemetry.gr Extended geo format examples]
==Notes==
==Notes==
# Umberto Eco, A Theory of Semiotics, 1976
# Umberto Eco, A Theory of Semiotics, 1976
Line 217: Line 241:


==Further discussion==
==Further discussion==
Comments and criticism about this page:
Pages for discussing this proposal:


* [[4d brainstorming]]
* [[4d implementation notes]]
</div>
</div>

Revision as of 18:16, 23 January 2007

This page and effort is failing to follow the microformats process. If you are the author of this page, please join the #microformats IRC channel and/or microformats-discuss mailing list so that the community can help walk you through the process. - Tantek

4d: A geo microformat alternative proposal

The term 4d stands for four dimensions and is used interchangeably with spacetime in this page, as heaving the same meaning. When in bold, it means the proposed microformat 4d.

Editor/Author
DimitriosZachariadis 17:03, 17 Jan 2007 (PST)
Page under construction

Abstract

A compact microformat for defining locations and events is proposed, as an alternative for the draft geo microformat. A tolerant five part, semicolon separated, spacetime and reference-system value, is argued to be sufficient to provide accurate information for uniquely identifying a place or an event in a four dimensional universe.

 

Introduction

Spacetimes are the arenas in which all physical events take place — for example, the motion of planets around the Sun may be described in a particular type of spacetime, or the motion of light around a rotating star may be described in another type of spacetime. The basic elements of spacetime are events. In any given spacetime, an event is a unique position at a unique time. Examples of events include the explosion of a star or the single beat of a drum.Spacetime, Wikipedia (annotation by the author)

 

LOCATION and geo referencing microformats proposed on this site, namely geo, luna and mars have at present (Jan 2007) a status of draft. Dealing with the issue of geo tagging requires a consensus on the issues of importance, if the microformat is to be successful and used without problems. To that extend, a proposal for a new microformat might not be superfluous, if it can present and offer for discussion some of the issues at hand. With that ambition, the 4d microformat is presented and discussed herein.

Brief discussion

Most of the location related information, whether about the Earth or another celestial body, have a time related aspect attached; historical places and events, geographical features, but also street names and addresses are tightly related to an act or an observation made at some point in time; addresses used today may have not been in use a century ago (assuming the place identified by the coordinates did exist), or may well change to something different tomorrow. Landmarks existing for centuries have an age, which means they have a birthday, but they may also one day disappear.

A vast amount of information used by people on a daily basis in the web is in fact an aggregation of events; stories and descriptions are most of the time nothing more than annotations of events. As such, most of this information can be accurately tagged, stored and used for as long as it exists, if its spacetime dimensions are known.

Default values and ambiguities

Disambiguation of the values used for tagging is an important issue, if the data tagged are to be valid, accurate and and useful outside the assumptions made at the time of their creation.

Omitting dimensions from a 4d coordinate system introduces assumptions about their default values. To demonstrate the issues that need to be dealt with, the following example of a markup, tagged with the geo microformat, might prove useful:

In 1687, a Turkish ammunition dump 

<a class="geo" href="http://maps.google.com/maps?q=37.971508,23.72658&ie=UTF8&z=18&ll=37.971508,23.72658
&spn=0.002584,0.006083&t=k&om=1&iwloc=addr">
inside the building
 <abbr class="latitude" title="37.971508"></abbr>, 
 <abbr class="longitude" title="23.72658"></abbr>
</a> 

was ignited by a Venetian cannonball. The resulting explosion severely damaged 
the Parthenon and its sculptures.

which may be rendered as:

In 1687, a Turkish ammunition dump inside the building was ignited by a Venetian cannonball. The resulting explosion severely damaged the Parthenon and its sculptures. Wikipedia, The Parthenon

In the case of the markup above, a human reader would assume that the coordinates involved in the code have been taken using WGS86, the most known and used datum today, due to its global validity and the proliferation of the GPS receivers. The ambiguity of altitude leads to an assumption of a default value of 0, which is acceptable for 2D cartography. No assumption can be made about time.

Verbosity

If the geo portion of the above markup is reduced to:

<a class="geo" href="http://maps.google.com/maps?q=37.971508,23.72658&ie=UTF8&z=18&ll=37.971508,23.72658
&spn=0.002584,0.006083&t=k&om=1&iwloc=addr">
inside the building
 <abbr class="latitude" title="37.971508"></abbr>, 
</a> 

the markup becomes useless for identifying locations, since it no more represents a location (but rather a geometric locus). If this is the case, then it seems that there is no point in having latitude and longitude defined by separate tags; indeed, the meaning of a coordinate is that it is an ordered list of numbers, or a tuple. Wikipedia, Coordinates. RFC2426[2] also specifies the GEO type as a single lat;long entity.

It could be argued that having a simpler, albeit verbose, format, helps content formating tools like XSLT processors, locate data easier. However, Microformats are a way of adding simple markup to human-readable data items such as events, contact details or locations, on web pages, so that the information in them can be extracted by software and indexed, searched for, saved, cross-referenced or combined. Microformats are not meant to help format content for humans, but to help machines gather information in a Semantic Web. On the other hand, a machine can split the data of a 4d tag in one single line of code.

Time

As argued above, the inclusion of a time dimension in geo markup can add significantly to the semantics of a piece of geo information, as it moves the focus of geo tagging from the realm of two dimensional cartography to the realm of events.

This should come as no surprise: events are about stories; cartography is about navigation. People are interested in stories, news and events; few people can successfully navigate using a map and even fewer are interested in navigation and cartography as a science or art. Geographic coordinates shown in the text are quite useless without a map, and are even more useless if an electronic map is available for use. Humans use names to identify places, not numbers. The reason there is a need for showing geographic coordinates in text, is mostly to help humans manually identify places on maps. If this can be done electronically, then numbers don't seem to matter.

A human visiting the page with the markup above (which was chosen for the length of the time dimension and the connotations involved), will have a chance to read the text (and the year of the event, which however is un-tagged), click at the link and get a Google Map centered at the Acropolis and the Parthenon. Semantic connotations for humans enhance their understanding of information presented to them.[1] However, a machine seeking information in the Semantic Web, will have no way of finding out if it is the 5th century BC Athenian state or the contemporary Greek state that this particular piece of information is referring to. Semantic information about that particular markup that could otherwise be cataloged by the machine, will pass unnoticed.

Had this geo markup been amended with a time dimension, a robot crawling this and other similar pages could create a list of historical events, based on nothing else but the information provided by the 4d microformat.

Humans have learned to deal with time efficiently, in their locality, through the use of clocks. Wrist watches remind people of upcoming events in their lives. An event in a remote place is more difficult to conceive, but not entirely impossible. Although it involves a simple addition or subtraction, only people traveling a lot can do it with ease.

Counting time in multiple reference systems is however a difficult task. It might not be necessary for humans in their daily life, but it is important when dealing with information on a global, or universal basis. Different cultures, use different reference systems to tell the time. Islamic calendar These need to be taken into account in a Semantic Web.

In a similar manner, trying to addapt to a Martian reference system, while living on Earth, involves more than a simple addition/subtraction of a few hours. A Martian day, is not of the same duration as a Terran day, and the same is true for the duration of the seasons; a number of connotations, that would otherwise help in getting a gut feeling, fail helplessly.

The reference system

It should be noted that the assumption about the datum used in expressing the lat-long coordinates mentioned above, is not a trivial one: Only 20 years ago, the same coordinates would possibly point hundreds of meters away from the Parthenon, since the reference system used at that time was different than WGS84. Furthermore, assuming WGS84 was the datum for the markup above, these coordinates may not be accurate 10 years from today, when the WGS84 reference system will have been revised once again.

A markable indication of the importance of the reference system, when expressing geo coordinates, is the fact that the Greenwich Observatory, which was by definition the origin for the longitude coordinate for more than a century, lies now about 102.5m West of the WGS84 0.0 meridian, at N 51° 28' 36.71, W 0° 0' 5.18", (in WGS84 datum) according to Wikipedia, Prime_Meridian. Interestingly, Google maps and Wikipedia do not seem to agree on these coordinates map

It should be clear that, for a microformat to be able to convey accurate information, well defined and known reference systems should be used. By performing transformations among the various reference systems, the content referenced in one system can be understandable and usefull on another, on a global or universal basis.

Name convention

Naming a geo microformat 4d helps avoid the problem of the geo-centric (i.e. Earth bound) root of the word geo; 4d can be easily used on any celestial body for which a reference system, even rudimentary, has been defined. To that extend, Mars related content can be readily microformatted and displayed on Google Mars. Obviously, matters regarding reference systems of other celestial bodies require expert knowledge, however, reading the news on NASA's site, e.g. for Titan, Two Sides of Dunes, reveals that reference systems are in place for all celestial bodies visited by a man made spacecraft, and probably for a lot more than those.

4d is a rather common acronym; Google yields about 53.9 million hits, while for 3d it yields 310 million hits and for geo 82.9 million.

Specification

It is proposed that the 4d microformat be formed as follows:

Root Class Name

The root class name for a 4d location/event is 4d

Property List

The 4d microformat has the following no properties.

Value

The value of a 4d location/event resides in the title attribute of an (X)HTML tag as a semicolon separated 5-tuple:

v1;v2;z;t;u  where:

v1 is either latitude or x, depending on u, mandatory
v2 is either longitude or y, depending on u, mandatory
z is the altitude, optional
t is the time, optional
u is the reference system code, optional

Dimensions z, t, and u can be omitted. If abiguities arrise from such an omition, e.g. omiting the z and t dimensions but defining the u dimension, then the relevant field values must be left empty, e.g.: v1;v2;;;u

Default Reference System

The default reference system is WGS84 and the Gregorian calendar.

The time dimension is expressed in the ISO-8601 format ("YYYY-MM-DDThh:mm:ss.ssZ"), in any of its abbreviations and forms. W3C, Date and Time Formats and Wikipedia, ISO-8601

Meta data

The default reference system may be set, using the name and content attributes of the meta (X)HTML element, as follows:

<meta name="4d.reference" content="reference-system"/>

Default coordinate values

When a dimension is omitted, the following default values are implied:

u: WGS84
v1: latitude, expressed in decimal degrees, no default
v2: longitude, expressed in decimal degrees, no default
z: altitude, expressed in meters, defaults to 0.0
t: time, no default

The default reference system for an (X)HTML page can be set by using meta data properties.

It is strongly recommended that web pages include a meta data element that defines the default reference system, in their HTML head section. The inclusion of the meta data element ensures the validity of the 4d data for as long as the page exists, while keeping 4d values compact. By adding the 4d metadata element, a conversion from the geo microformat to the 4d would only require the change of the root class, from geo to 4d.

Reference systems

Indicative reference systems include:

  • UTM:zone
    • v1 is x, expressed in meters
    • v2 is y, expressed in meters
    • t is expressed in ISO-8601

Examples

The markup used in the discussion, transferred in the 4d microformat:

In 1687, a Turkish ammunition dump 

<a class="4d" href="http://maps.google.com/maps?q=37.971508,23.72658&ie=UTF8&z=18&ll=37.971508,23.72658
&spn=0.002584,0.006083&t=k&om=1&iwloc=addr">
 inside the building
 <abbr class="4d" title="37.971508;23.72658"></abbr>
</a> 

was ignited by a Venetian cannonball. The resulting explosion severely damaged 
the Parthenon and its sculptures.

Example 1

Hidden 4d coordinates, no content

The Parthenon was ruined by a Venetian cannonball in 1687
<abbr class="4d" title="37.971508;23.72658;;1687"></abbr>

Example 2

Hidden 4d coordinates, free text content

<span class="4d" title="37.971508;23.72658;;1687">
The Parthenon was ruined by a Venetian cannonball in 1687
</span>

may be rendered as:

The Parthenon was ruined by a Venetian cannonball in 1687

Example 3

Visible 4d coordinates

<abbr class="4d" title="37.971508;23.72658;;1687">N 37° 58' 17.43, E 23° 43' 35.69</abbr>

may be rendered as:

N 37° 58' 17.43, E 23° 43' 35.69

Example 4

Minimum HTML page:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <meta name="4d.reference" content="WGS86"/>
  </head>
<body>
  <div class="4d" title="51.476864;-0.000518">
  The Greenwich Observatory
  </div>
</body>
</html>

Example 5

A fictitious Mars reference system, using actual Mars coordinates from Google Mars:

<span class="4d" title="18.302380;-133.472900;;;MARS:J2000">
Olympus Mons, Mars: The highest mountain in the solar system.
</span>

rendered as:

Olympus Mons, Mars: The highest mountain in the solar system.


Real world example

[http:// A crafted page with the examples appering here and a small map demonstration]

Notes

  1. Umberto Eco, A Theory of Semiotics, 1976
  2. RFC2426
  3. W3C, Date and Time Formats
  4. Wikipedia, ISO-8601

Further discussion

Pages for discussing this proposal: