[postgis-users] ST_DWithin with radius 0.000001

[nguyen liem]

Hi Nicklas

sr for the mistake  ... field but it *was not* improve the perofrmance for
ST_intersect

Cheers

On Tue, May 25, 2010 at 3:53 PM, nguyen liem <liemnguyendl at gmail.com> wrote:

> 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.
>
>


-- 
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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