# [postgis-users] Check identical point

Nicklas Avén nicklas.aven at jordogskog.no
Sat May 22 06:46:04 PDT 2010

```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 at 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
>>>>

>>
>>
>>
>>
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