[postgis-users] Re: Bounding Circle instead of Bounding Box

Nico Mandery nicomandery at googlemail.com
Tue Sep 18 02:20:16 PDT 2007


Hi Shane,

sorry for the delay, i had no access to the Internet for while.

here is a short definition of the term buffer from
http://www.fws.gov/data/IMADS/glossary.htm :

buffer - A zone of a specified distance around coverage features. Both
constant- and variable-width buffers can be generated for a set of
coverage features based on each feature's attribute values. The
resulting buffer zones form polygons-areas that are either inside or
outside the specified buffer distance from each feature. Buffers are
useful for proximity analysis (e.g., find all stream segments within
300 feet of a proposed logging area).

In this context you could create a buffer with a distance X and a
buffer with a distance Y around the point, and then look for point
wicht are in the in the area of (bufferX-bufferY).

nico

>Could you reply with a URL to what buffers are and how they would be
>used in this context? I'm >totally unfamiliar.
>
>
> On 9/9/07, Nico Mandery < nicomandery <at> googlemail.com> wrote:
>> Hi Rainer,
>>
>> You could could use a buffer instead of bounding boxes.
>> Just an idea
>>
>> Nico
>>
>> Am Sonntag 09 September 2007 schrieb postgis <at> jochem.name:
>> > Hi,
>> >
>> > what I want to do is finding certain features in some distance around a
>> > certain point. Those features should be located in some corridor between X
>> > and Y km around this point. Currently I've solved this problem by
>> > computing two bounding boxes of X and Y km around the point and taking the
>> > difference of those. So far so good.
>> >
>> > But I don't want to have some quadratic box but a real circle - is there
>> > any way to achieve this?
>> >
>> > Best regards,
>> >  Rainer
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