Geometry Boost List: [ggl] point on the border and within ?

Subject: [ggl] point on the border and within ?
From: Mateusz Loskot (mateusz)
Date: 2011-10-05 13:42:55

On 05/10/11 15:33, Adam Wulkiewicz wrote:
> 2011/10/5 Aleksandar Babic<aleksandarb_at_[hidden]>
>>
>> Hei, I have the following problem - detecting point on the border
>> of ring, The code is like this: [...] I'm always getting NO. Am I
>> doing something wrong .. or this is a bug?
>
> Hi,
>
> within() returns false for borders.

There are many subtle differences between those predicates.
Here is a good summary of them:

http://lin-ear-th-inking.blogspot.com/2007/06/subtleties-of-ogc-covers-spatial.html

and PostGIS documentation is a good source of graphical examples:

http://www.postgis.org/docs/ST_Contains.html
http://www.postgis.org/docs/ST_Within.html

Also, I think it's better to speak of boundaries, not borders.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org
Member of ACCU, http://accu.org