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List: postgis-users
Subject: Re: [postgis-users] Check identical point
From: Nicklas_Avén <nicklas.aven () jordogskog ! no>
Date: 2010-05-22 13:46:04
Message-ID: 201005221346.o4MDk47c031975 () mail-core ! space2u ! com
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Oh, I saw my own typo (forget the arguments for pointdistance3d). the query should be
Select * from table1, table2
where table1.the_geom &&ST_Expand(table2.the_geom, 0.1) and
table2.the_geom && ST_Expand(table1.the_geom, 0.1) and
pointdistance3d(table1.the_geom, table2.the_geom)<=0.1;
/Nicklas
2010-05-22 Nicklas Avén wrote:
Hallo
>
> The ST_DWithin fuction will only check the 2d distance and not care it the points \
> are far from each other in z direction.
> If you need to also check they are close in z-direction I guess the easiest way is \
> to calculate the 3d distance between the points with Pythagorean theorem. The \
> cleanest maybe is to make a function of it like this:
>
> create or replace function pointdistance3d(p1 geometry, p2 geometry)
> returns double precision as
> $$
> select sqrt((st_x($1)-st_x($2))^2 + (st_y($1)-st_y($2))^2 + (st_z($1)-st_z($2))^2);
> $$
> language 'sql';
>
>
> then to get some speed of it you can use st_dwithin to do a first index-based \
> search. That is as said only a 2d calculation, but if the distance is more than \
> your tolerance in 2d it will be also in 3d.
> I think the most effective way of doing this is to only do the bounding box \
> comparison that is built into st_dwithin and then go straightly to the 3d \
> calculation. That would look something like this if we use the tolerance 0.1 meters \
> (requires based coordinate sytem):
> Select * from table1, table2 where table1.the_geom && \
> ST_Expand(table2.the_geom, 0.1) and table2.the_geom && \
> ST_Expand(table1.the_geom, 0.1) and pointdistance3d<=0.1;
> Hope that helps
>
> Nicklas
>
>
> Try:
> > ST_DWithin(point1, point2, 0.00001)
> >
> > -F
> >
> > > >
2010/5/22 eehab hamzeh <eehab40@hotmail.com>
> > > >
Hello
> >
> > I want to check if two points are identical, the points has x,y,z coordinates and \
> > they are not exactly the same, i need to check the intersection between them with \
> > tolerance value. any direction of how to do that.
> > Thank
> >
> > kind regards
> > > >
> >
> >
> >
> >
> > Hotmail: Powerful Free email with security by Microsoft. Get it now.
> > _______________________________________________
> > postgis-users mailing list
> > postgis-users@postgis.refractions.net
> > postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
> >
[Attachment #5 (unknown)]
<html>
<head>
</head>
<body>Oh, I saw my own typo (forget the arguments for pointdistance3d). the query \
should be<br /> <br />
Select * from table1, table2 <br />
where table1.the_geom &&
ST_Expand(table2.the_geom, 0.1) and<br />
table2.the_geom && ST_Expand(table1.the_geom, 0.1) and <br />
pointdistance3d(table1.the_geom, table2.the_geom)<=0.1;<br />
<br />
/Nicklas<br />
<br />
2010-05-22 Nicklas Avén wrote:<br />
<br />
Hallo<br />
><br />
>
The ST_DWithin fuction will only check the 2d distance and not care it the points \
are far from each other in z direction.<br /> ><br />
>
If you need to also check they are close in z-direction I guess the easiest way is \
to calculate the 3d distance between the points with Pythagorean theorem. The \
cleanest maybe is to make a function of it like this:<br /> ><br />
><br />
>
create or replace function pointdistance3d(p1 geometry, p2 geometry)<br />
>
returns double precision as<br />
>
$$<br />
>
select sqrt((st_x($1)-st_x($2))^2 + (st_y($1)-st_y($2))^2 + \
(st_z($1)-st_z($2))^2);<br /> >
$$<br />
>
language 'sql';<br />
><br />
><br />
>
then to get some speed of it you can use st_dwithin to do a first index-based \
search. That is as said only a 2d calculation, but if the distance is more than your \
tolerance in 2d it will be also in 3d.<br /> ><br />
>
I think the most effective way of doing this is to only do the bounding box \
comparison that is built into st_dwithin and then go straightly to the 3d \
calculation. That would look something like this if we use the tolerance 0.1 meters \
(requires based coordinate sytem):<br /> ><br />
>
Select * from table1, table2 where table1.the_geom && \
ST_Expand(table2.the_geom, 0.1) and<br /> >
table2.the_geom && ST_Expand(table1.the_geom, 0.1) and \
pointdistance3d<=0.1;<br /> ><br />
>
Hope that helps<br />
><br />
>
Nicklas<br />
><br />
><br />
>
Try:<br />
>
> ST_DWithin(point1, point2, 0.00001) <br />
>
><br />
>
>-F<br />
>
><br />
>
>>
>
<div>2010/5/22 eehab hamzeh <<a>eehab40@hotmail.com</a>><br />
>
>
>
>
<div>
Hello <br />
>
><br />
>
>I want to check if two points are identical, the points has x,y,z coordinates and \
they are not exactly the same, i need to check the intersection between them with \
tolerance value. any direction of how to do that.<br /> >
><br />
>
>Thank <br />
>
><br />
>
>kind regards<br />
>
>>
>
<div><br />
>
><br />
>
><br />
>
><br />
>
><br />
>
><hr />
Hotmail: Powerful Free email with security by Microsoft. <a \
href="https://signup.live.com/signup.aspx?id=60969" target="_blank">Get it \
now.</a></div>
</div>
<br />
>
>_______________________________________________<br />
>
>
postgis-users mailing list<br />
>
><a>postgis-users@postgis.refractions.net</a><br />
>
><a href="http://postgis.refractions.net/mailman/listinfo/postgis-users" \
target="_blank">postgis.refractions.net/mailman/listinfo/postgis-users</a><br /> >
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