Re: [uf-discuss] Geo precision

[Ben O'Neill]

On 8/27/07, Ben Ward <[EMAIL PROTECTED]> wrote:

Since then the only additional information I've found is that Flickr
stores accuracy (as an integer) based on the zoom level of the map
when you place a photo. In fact, if you zoom all the way out and
place a photo you'll get a notice warning you that the location is
too approximate and the photograph won't show up at higher zoom  
levels.


I've been doing some work with Google's geocoder, encoding addresses
into co-ordinates for mapping purposes.

Google uses an 9-point enum that is specified as a
human-understandable scale rather than specific geographical terms:

0Unknown location.
1Country level accuracy.
2Region (state, province, prefecture, etc.) level accuracy.
3Sub-region (county, municipality, etc.) level accuracy.
4Town (city, village) level accuracy.
5Post code (zip code) level accuracy.
6Street level accuracy.
7Intersection level accuracy.
8Address level accuracy.


Flickr uses a 16 point system:

- World level is 1
- Country is ~3
- Region is ~6
- City is ~11
- Street is ~16

This is taken from the Flickr API 



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Re: [uf-discuss] Geo precision

[Ciaran McNulty]

On 8/27/07, Ben Ward <[EMAIL PROTECTED]> wrote:
> Since then the only additional information I've found is that Flickr
> stores accuracy (as an integer) based on the zoom level of the map
> when you place a photo. In fact, if you zoom all the way out and
> place a photo you'll get a notice warning you that the location is
> too approximate and the photograph won't show up at higher zoom levels.

I've been doing some work with Google's geocoder, encoding addresses
into co-ordinates for mapping purposes.

Google uses an 9-point enum that is specified as a
human-understandable scale rather than specific geographical terms:

0Unknown location.
1Country level accuracy.
2Region (state, province, prefecture, etc.) level accuracy.
3Sub-region (county, municipality, etc.) level accuracy.
4Town (city, village) level accuracy.
5Post code (zip code) level accuracy.
6Street level accuracy.
7Intersection level accuracy.
8Address level accuracy.

ref:
http://www.google.com/apis/maps/documentation/reference.html#GGeoAddressAccuracy

-Ciaran McNulty
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RE: [uf-discuss] Geo precision

[Farndon, Tony]

I have noticed Precision and Accuracy being mentioned in the same
context but I believe the two are not the same.

Accuracy (to me) is how close a point is located to it's actual real
earth location - getting the lat/lng of your house when using a map that
is zoomed to country level will not be as ACCURATE as getting the
lat/lng when the map is zoomed right into street level.

Precision (to me) is the scale at which you are trying to locate -
putting the coordiantes of New York is a PRECISION of city level, and
you could find many people using slightly different coordinates for New
York, but they are all _precise_ for that city.

My 2p.

Tony

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Re: [uf-discuss] Geo precision

[Ben Ward]

On 27 Aug 2007, at 01:19, Michael MD wrote:
I remember some discussion a while back about "fuzzy" locations ..  
but I

can't remember if anything was worked out.


No, nothing got worked out of that one.

Since then the only additional information I've found is that Flickr  
stores accuracy (as an integer) based on the zoom level of the map  
when you place a photo. In fact, if you zoom all the way out and  
place a photo you'll get a notice warning you that the location is  
too approximate and the photograph won't show up at higher zoom levels.


I'll see if I can find out what the range of accuracy numbers is, and  
what scale they correspond to.


Ben
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RE: [uf-discuss] Geo precision

[Michael MD]

>>The longitude and latitude values MUST be specified as decimal degrees
>>and should be specified to six decimal places.
>

What about approximate coordinates? - eg for something near a known city -
(still useful information but obviously not to be used for looking up street
addresses)

Still looking for good ways to relate city/place names to locations that do
not require external geocoding services which are unreliable with freeform
user-entered addresses.

I remember some discussion a while back about "fuzzy" locations .. but I
can't remember if anything was worked out.




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[uf-discuss] Geo precision

[Andy Mabbett]

In message <[EMAIL PROTECTED]>, Andy Mabbett 
<[EMAIL PROTECTED]> writes



The longitude and latitude values MUST be specified as decimal degrees
and should be specified to six decimal places.


That's interesting


It seems that draft-ietf-calsify-rfc2445bis-07.txt (i.e., the revision 
of iCalendar) proposes changing that MUST to a MAY.




(aka  ) N.B. page size is 1.6 Mb!

--
Andy Mabbett
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[uf-discuss] Geo precision (was: hCard multiple locations)

[Andy Mabbett]

In message 
<[EMAIL PROTECTED]>, Kevin 
Marks <[EMAIL PROTECTED]> writes


>The longitude and latitude values MUST be specified as decimal degrees
>and should be specified to six decimal places.

That's interesting; it's clearly not suitable when giving the 
coordinates for very large sites like a county or a park, where 
precision to 1 metre is unwarranted; nor for giving very precise 
coordinates for, say, the location of the camera taking a picture of a 
single flower or insect. It's certainly not what's used in practice.


Perhaps the Geo spec, and those of the other microformats which use it, 
should allow fewer or more decimal places, and require parsers to 
convert to six places when exporting as a vCard? Or perhaps a revision 
to the vCard spec is required?


The spec does, though, emphasise the points I've always made; the number 
of decimal place for latitude and longitude should be equal; and 
trailing zeroes are significant.


--
Andy Mabbett
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