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Thread: indexing lat lon

indexing lat lon

From
"Jonathan Raemdonck"
Date:
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..
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Re: indexing lat lon

From
Tom Lane
Date:
"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

Re: indexing lat lon

From
Oleg Bartunov
Date:
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