[postgis-users] finding whether an object lies in vicinity of another object

Tom van Tilburg tom.van.tilburg at gmail.com
Mon Oct 8 06:02:54 PDT 2012


Hi Tasneem,

You will have to create a geometry first before you can use postgis 
functions. Just 2 columns with coordinates are not enough (you're very 
close though).
I would recommend to do some reading in the manual, especially here:
http://postgis.refractions.net/documentation/manual-2.0/PostGIS_FAQ.html#id605751

It boils down to adding a column with

	SELECT AddGeometryColumn('', 'yourtable','geom',-1,'POINT',2);

and then filling the column with
     UPDATE yourtable SET geom = ST_SetSrid(ST_MakePoint(xcolumn, 
ycolumn),4326)
     (see: 
http://postgis.refractions.net/documentation/manual-2.0/ST_MakePoint.html)

Besides that: most likely you want to use ST_DWithin, it's supposed to 
be faster than ST_Within.

Cheers,
  Tom

On 8-10-2012 14:40, tasneem dewaswala wrote:
> Hello,
>
> I am developing an application to find whether two cars are in each 
> other communication range or not.
> I have two tables like receiver and transmitter. i would like to know 
> if receiver is in 100 meters range of transmitter or not.
> Since i am using PostgreSQL first time, i donno much about its 
> functions and commands, but i have found that there is ST_Within(), 
> which can be used for my work. I tried but it gives me lot of errors, 
> probably because of data types of my latitude and longitude. they are 
> in two different columns with datatype as double precision.
>
> please tell me what is wrong, and how should i use ST_WITHIN for my 
> work. Or tell me any other way of knowing if two objects are in range 
> of each other.
>
>
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