I'm interested in getting the coverage item better defined.
A lot of Web pages are associated with a particular place (home pages for
businesses that have a physical storefront, etc.) and I think it
would be useful to be able to do geographic filtering, as well as
facilitate such things as automatic map generation and trip planning.
At the same time, I am concerned that the scheme does not get too
complicated, at least as far as data entry is concerned. In many cases
a simple position is sufficient, rather than a range. This might be
generated as a collapsed case by a script. Also, it may be necessary
to define a datum such as WGS84, or to allow a datum to be specified.
An uncertainty in measurement may also be required.
Related work:
http://www.nlanr.net/Viz/Mbone/rfc1876bit.html
ftp://ds.internic.net/rfc/rfc1876.txt
http://www.kei.com/homepages/ckd/dns-loc.html
An effort is underway to map the Mbone (and Internet). This RFC describes
a method of encoding positional information in a DNS record. The
record describes a sphere at a given latitude/longitude/altitude (WGS84
datum) with a given diameter, horizontal uncertainty and vertical
uncertainty. e.g. LOC 42 21 54 N 71 06 18 W -24m 30m
a 30 metre sphere centered at 42D21'54"N 71D06'18"W 24m below datum.
(The RFC specifies a binary data record in the DNS)
It might be useful to adopt this as an allowable coverage record, seeing
as someone has already submitted the RFC. Alternatively, ASCII floats
could be used as perhaps less ambiguous than the space-delimited form
above, e.g.
LOC.COVERAGE 42.365 -71.105 -24.0 30.0 200.0 5.0
specifying the same location, with a 200 meter horizontal uncertainty
and 5 meter vertical uncertainty.
For a search engine, while it is possible to deduce which format is used
from the content, as is done for HTTP date records, it is preferable
to either define the format rigorously or provide a schema name which
defines it.
GPS sets, incidentally, generate a variety of different electronic records
for downloading, e.g.
http://vancouver-webpages.com/cgi-bin/divelocate?50D7.60N+125D9.06W:Cortes
although NMEA0183 is standard for inter-device communication. Again,
most of these don't support altitude information, being originally
designed for use at sea. NMEA does, however, support the GGA record, viz.
$--GGA,hhmmss.ss,llll.ll,a,yyyyy.yy,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh
which does include altitude information, but is probably overkill
as it includes satellite information ...
Andrew Daviel mailto:[log in to unmask]
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