[postgis-users] Circle

[Paul Ramsey]

ST_Buffer is like blowing up a balloon... it takes the input and makes
it uniformly puffier in all directions.  Puffing up a point makes a
circle, puffing up a line makes a hotdog, puffing up a polygon
makes... a puffier polygon.
You can also use negative values on polygons to suck them down to
smaller versions of themselves.

On Fri, Jun 13, 2008 at 4:58 PM, Michael Smedberg
<Michael.Smedberg at redfin.com> wrote:
> FYI, you can find some documentation on ST_Buffer at
> http://postgis.refractions.net/docs/ch06.html
>
> It reads:
>
> ST_Buffer(geometry, double, [integer])
>
>    Returns a geometry that represents all points whose distance from
> this Geometry is less than or equal to distance. Calculations are in the
> Spatial Reference System of this Geometry. The optional third parameter
> sets the number of segment used to approximate a quarter circle
> (defaults to 8).
>
>    Performed by the GEOS module
>
>    Do not call with a GeometryCollection as an argument
>
>    OGC SPEC s2.1.1.3
>
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
> Pawley
> Sent: Friday, June 13, 2008 4:54 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Circle
>
> Is that the only function of the buffer - to create a circle?
>
> Can the buffer modify other functions. If so - what is the criteria?
>
> Bob
> ----- Original Message -----
> From: "Paul Ramsey" <pramsey at cleverelephant.ca>
> To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
> Sent: Friday, June 13, 2008 4:33 PM
> Subject: Re: [postgis-users] Circle
>
>
>> Try it and see :)
>> It constructs a circular-shaped polygon around the point.
>> P
>>
>> On Fri, Jun 13, 2008 at 4:23 PM, Bob Pawley <rjpawley at shaw.ca> wrote:
>>> I'm interested in what the buffer actually does.
>>>
>>> Bob
>>>
>>> ----- Original Message ----- From: "Paul Ramsey"
>>> <pramsey at cleverelephant.ca>
>>> To: "PostGIS Users Discussion"
> <postgis-users at postgis.refractions.net>
>>> Sent: Friday, June 13, 2008 3:46 PM
>>> Subject: Re: [postgis-users] Circle
>>>
>>>
>>>> ST_Buffer(ST_MakePoint(x,y),r)
>>>>
>>>> On Fri, Jun 13, 2008 at 3:35 PM, Bob Pawley <rjpawley at shaw.ca>
> wrote:
>>>>>
>>>>> What is the best way of creating a circle?
>>>>>
>>>>> Mu PostgreSQL Developes Handbook susy it should be - point and
> radius.
>>>>>
>>>>> Postgis doesn't seem to have this function.
>>>>>
>>>>> Bob
>>>>> _______________________________________________
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>>>>>
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