[postgis-users] spheroid bounding box calculation

[Stephen Woodbridge]

Oh, and the basic sql query would be:

select * from poi_table where st_within(setsrid(makepoint(x,y),4326), 
the_geom, radius) order by st_distance(setsrid( makepoint(x,y),4326), 
the_geom) asc limit n;

(x,y) == (lon, lat)
radius == is your initial search radius
n == is your limit on results

-Steve

Stephen Woodbridge wrote:
> steve enzer wrote:
>> I'm facing a similar issue; a huge postgis database with a point
>> column, trying to find a clean query to bring back the nearest n
>> results to a point.  Why isn't that easy? Or is it?
> 
> The problem is that the nearest n points is not well defined in spatial 
> terms. For example think about the difference between rural Wyoming and 
> downtown Manhattan!
> 
> Typically to make a query fast you need to use and index and that means 
> you need a bounding box that specifies your search distance. But the 
> bbox that is good for Manhattan may be too small for Wyoming.
> 
> One strategy is to search at a given small radius and see if you have 
> enough results, if not double the search radius and redo the query. 
> While this may seem costly, it is in fact very fast because postgresql 
> is very good at caching results and pages in memory.
> 
> Hope this helps,
>   -Steve
> 
>> I'm using georuby and spatial adapter.
>>
>> Steve
>>
>> On Thu, Jul 23, 2009 at 10:01 AM, Jeff Davis<pgsql at j-davis.com> wrote:
>>> On Thu, 2009-07-23 at 08:58 -0700, Paul Ramsey wrote:
>>>> Hopefully GEOGRAPHY will retire all these requirements once and for
>>>> all :)
>>> Is that something under development? I'm new to these lists, so I
>>> haven't been following.
>>>
>>> Regards,
>>>        Jeff Davis
>>>
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