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 <u...@oss4u.com> > ** > > > > 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. > > 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. > > > > 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. > > > > 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... > > > > 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.. > > > > Uwe > > > > > > > > > > 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 > > > > -- Olivier Chaussavoine
