Обсуждение: indexing lat lon
I have the following situation:
I'm developing an reverse geocoder, so input is lat/lon coordinate and
output is the nearest textual location.
I have a database of +- 2 000 000 records that contains lat/lon and full
name of the location.
These are the steps I take now:
1 'draw' a box around the lat/lon position we have as input
2 search the DB for all the points in this box
3 measure the distance to each point in the box
This works fine, but step 2 takes too lang for obvious reasons...
select * from table
where lat between box_point1_lat and box_point2_lat
and lon between box_point1_lon and box_point2_lon;
This would require a seq scan for but indexing the table doesn't help much
either (factor 2) ...
Is there a good way of indexing the lat/lon column so lookup is faster? I
have looked at PostGis but didn't think it would give a good solution in
this context (correct me if I'm wrong)
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"Jonathan Raemdonck" <jonathan_raemdonck@hotmail.com> writes:
> These are the steps I take now:
> 1 'draw' a box around the lat/lon position we have as input
> 2 search the DB for all the points in this box
> 3 measure the distance to each point in the box
Right. All you need is an index amenable to step 2.
> Is there a good way of indexing the lat/lon column so lookup is faster?
Yeah, you can store the lat/long as a point, build an rtree index on it,
and use box-overlap as the indexable operator. I seem to recall that
you actually have to store the lat/long as a box of zero size to get
this to work with the present set of rtree-indexable operators. If you
look in the archives you will find some previous similar cases.
regards, tom lane
Jonathan, you may try contrib/pgsphere http://www.pgastro.org/cgi-bin/wiki.pl?pgSphere On Sun, 27 Jun 2004, Jonathan Raemdonck wrote: > I have the following situation: > > I'm developing an reverse geocoder, so input is lat/lon coordinate and > output is the nearest textual location. > I have a database of +- 2 000 000 records that contains lat/lon and full > name of the location. > > These are the steps I take now: > 1 'draw' a box around the lat/lon position we have as input > 2 search the DB for all the points in this box > 3 measure the distance to each point in the box > > This works fine, but step 2 takes too lang for obvious reasons... > select * from table > where lat between box_point1_lat and box_point2_lat > and lon between box_point1_lon and box_point2_lon; > > This would require a seq scan for but indexing the table doesn't help much > either (factor 2) ... > > Is there a good way of indexing the lat/lon column so lookup is faster? I > have looked at PostGis but didn't think it would give a good solution in > this context (correct me if I'm wrong) > > _________________________________________________________________ > Plannen om een nieuwe computer te kopen? Kijk eens hier.. > http://www.msn.be/shopping/dell_bis/ > > > ---------------------------(end of broadcast)--------------------------- > TIP 8: explain analyze is your friend > Regards, Oleg _____________________________________________________________ Oleg Bartunov, sci.researcher, hostmaster of AstroNet, Sternberg Astronomical Institute, Moscow University (Russia) Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/ phone: +007(095)939-16-83, +007(095)939-23-83