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

[Paragon Corporation]

Read first chapter of our book (which is a free download). The examples at
the end covers exactly what you are asking.
 
http://www.manning.com/obe/
 
Also if you don't know much about SQL, the free Appendix C covers the
fundamentals of SQL.
 
Leo
http://www.postgis.us
 
 

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of tasneem
dewaswala
Sent: Tuesday, October 09, 2012 1:22 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] finding whether an object lies in vicinity of
another object


Hello, 
Thank you for your reply.

I have added a geometry column to my existing table.
But i am facing problems in updating that column.
since i have thousands of row, it would not be feasible to update each row
at a time. 
what should i do to update all geometries at once? 


On Mon, Oct 8, 2012 at 6:32 PM, Tom van Tilburg <tom.van.tilburg at gmail.com>
wrote:


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#id6
05751

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.

 

_______________________________________________

postgis-users mailing list

postgis-users at postgis.refractions.net

http://postgis.refractions.net/mailman/listinfo/postgis-users



_______________________________________________
postgis-users mailing list
postgis-users at postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-users/attachments/20121009/0af46add/attachment.html>