[postgis-users] ST_DWithin with radius 0.000001

[nguyen liem]

Hi Nicklas

my dataset about 100.000 rows and after run my query i get about 15.000
rows. I has created index for "geom" field but it was improve the
perofrmance for ST_intersect

I used SRID 4326, but I don't know how to convert from degree to meter.

Cheers

On Tue, May 25, 2010 at 3:43 PM, Nicklas Avén <nicklas.aven at jordogskog.no>wrote:

> Ok
>
> The distance of 0.00001 degree in east west direction will vary depending
> on how far from the equator you are.
>
> How many points is there in your dataset?
>
> Do you see if the index is used?
>
> /Nicklas
>
>
> 2010-05-25 nguyen liem wrote:
>
> 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.
> >
> >----------------------------------------------------------------------------
> > >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          : 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          : 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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