Re: earthdistance

I did not found any geographic indexing with earthdistance, and need it.

The need I have is simple:
"is the distance between two (lat,long) positions less than X km?"
the model used for the shape of the earth should be related to the
precision of lat,lon, and most sources are imprecise. The spherical model
should be enough.

How wrong I am to think that:
* postgres contains a circle object where distance is the hypothenuse. The
spherical problem using lat,long is also bidimensional. We could /just use
haversine distance instead of hypothenuse.
* gist and b-tree bidimensional indexing does not need to be changed to
fulfill this need.

2013/8/10 Uwe Schroeder <uwe(at)oss4u(dot)com>

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> How accurate do you need it? My website has a lot of "local" listing stuff
> based on a distance from the viewer and I use the earthdistance module in
> contrib to do it.
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> Given, it's not accurate enough to calculate a surgical missile strike,
> but for "within 20 miles" type of things it's good enough - give or take a
> mile.
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> The problem I have is to determine the location of the viewer/poster.
> Aside from asking precice lat/long coordinates (which no user will have any
> clue about), the next best thing is to rely on smartphones and their GPS -
> but what of regular browser/computer users? When I let google map my
> location it shows as San Francisco - which is about 56 miles off. So
> network location makes no sense for this.
>
> I'm using a zipcode based geographical mapping, which already has flaws
> since a zipcode is an area, not a point. The commonly available zipcode
> databases give you the geographical center of the zipcode - which certainly
> will be some distance off from the real location.
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> I found that the inaccuracies work for my application - nobody cares about
> a few more or less miles when looking for something. The advantage is that
> it also protects the privacy of the poster to some degree - nobody really
> needs to know exactly where the post originated...
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> If "openbarter" is what I think it is (kinda craigslist just with
> bartering), I think a few miles off won't make a difference. Chances are,
> your members won't divulge their true location anyways. We have members
> from South Africa using a US zipcode - which is what ... 5000 miles off?
>
> Earthdistance is definitely easy to deal with - just give a
> latitude/longitude and off you go..
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> Uwe
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> On Fri, 08/09/2013 09:29:49 PM Olivier Chaussavoine wrote:
>
> I develope a project openbarter that needs to match objects based on a
> maximum distance between their positions on earth. I saw that the
> documentation of the extension earthdistance was interesting, but the
> promise was not in the code. It would be nice to have these functions
> available independently of sophisticated geographic systems. There is a
> circle object for flat two dimensional space, but earth deals with
> spherical caps. It would not be exact but enough to suppose that earth is a
> sphere and that all dimensions latitude, longitude and distance are in
> radian.
> What would need to be done to adapt the circle type to a new type
> 'spherical cap' that would allow simple geographic indexing?
>
> --
> Olivier Chaussavoine
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--
Olivier Chaussavoine