[postgis-users] ST_DWithin with radius 0.000001

[nguyen liem]

Hi Nicklas

Actually the points can be outside the polygon and returning true but it can
be tolerance about 1 meters outside.
I'm using SRID: 4326. I would like to know 0.00001 with the projection 4326
is equal 1 meter or not ?

I used ST_Intersects (geom, geometry); but it's really slow, I don't know
why.
I also used ST_Dwithin (geom, geometry, 0) and the result is empty, i
couldn't found any neighbour.

Cheers

On Tue, May 25, 2010 at 3:22 PM, Nicklas Avén <nicklas.aven at jordogskog.no>wrote:

> Hallo
>
> What you are doing with ST_Dwithin is to check if your geom and geometry
> have parts closer to (or exactly) 0.00001 mapunits from eachother. If you
> are using a meter based SRID then you are checking if they are within
> 0.00001 meters from eachother. So actually in this case your points can be
> just outside the polygon and returning true. If you want to use st_dwithin
> you should use 0 instead of 0.00001 . But I don't think that is any faster
> than ST_Intersects. The important thing in both cases is to have working
> spatial indexes.
>
> put an index on geom column in my_neighbour table and analyze the table.
>
> Create index idx_mn_geom
> on my_neighbour
> using gist(geom);
> analyse my_neighbour;
>
> Then try:
>
> SELECT id, geom
> FROM my_neighbour
> WHERE ST_Intersects (geom, geometry);
>
> I guess that is the best solution.
>
> Hope that helps
>
> Nicklas
>
>
> 2010-05-25 nguyen liem wrote:
>
> Hi all
> >
> >At the first time i used ST_Contains but it take a long time, so I used
> ST_Dwithin to improve the performance for the query statement but i don't
> know it is correct or not.
> >I would like to know my points are within in polygon or not:
> >
> >SELECT id, geom
> >FROM my_neighbour
> >WHERE ST_Dwithin (geom, geometry, 0.00001)
> >
> >geometry: is a polygon(input parameter).
> >0.00001: I means the radius of geometry is 1 meters, is it right?
> >
> >
> >Cheers.
> >
> >--
> >Liem Nguyen
> >Developer
> >Axon Active Corp.
>
> >----------------------------------------------------------------------------
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> >Fax                  : +84 38 811 3489
> > Mobile Phone  : +84 168 994 8897
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> > Web Site          : axonactive.vn
>
> >Address           : 87 Thang Long Street,Gate 2 Ward 4,
> >                          Tan Binh District, HCM city, Vietnam.
> >
> >
>
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-- 
Liem Nguyen
Developer
Axon Active Corp.
----------------------------------------------------------------------------
Direct Line      : +84 38 948 4645
Fax                  : +84 38 811 3489
Mobile Phone  : +84 168 994 8897
Skype ID         : liemnguyendl2204
Email               : liem.nguyen at axonactive.net / liemnguyendl at gmail.com
Web Site          : http://axonactive.vn
Address           : 87 Thang Long Street,Gate 2 Ward 4,
                         Tan Binh District, HCM city, Vietnam.
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