[postgis-devel] [PostGIS] #413: ST_Single_Sided_Buffer added

Martin Davis mbdavis at refractions.net
Fri Feb 19 12:49:28 PST 2010


As I read it, the ArcGIS Buffer method is defined to return only 
polygons.  This is a different situation than ST_OffsetCurve, which 
returns lines.

I think that having the ST_OffsetCurve name is good, to indicate that 
the function returns linework.  That allows users to conceptualize the 
simple rule that ST_Buffer always returns polygonal geometry.

Pierre Racine wrote:
> In ArcGIS they pass one of the four following options:
>
> {FULL | LEFT | RIGHT | OUTSIDE_ONLY}
>
> http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Buffer_%28Analysis%29
>
> Ex.:
>
> gp.buffer("roads.shp", "buffered_roads.shp", "Distance", "OUTSIDE_ONLY", "ROUND", "LIST", "Road_Type")
>
> The last two are of no interest for PostGIS. The ROUND is the same as ST_Buffer's endcap. Probably there should be a 4th option to ST_Buffer's buffer_style_parameters to indicate the surface occupied by the buffer:
>
> 'lineside=full|left|right|outside'
>
> You probably want to be ablt to do "right|outside" or "left|outside" at the same time.
>
> Probably, to completely fulfill rafalmag's needs, it would be nice to add "none" as endcap, so we don't get any end cap at all.
>
> Pierre
>
>   
>> -----Original Message-----
>> From: postgis-devel-bounces at postgis.refractions.net [mailto:postgis-devel-
>> bounces at postgis.refractions.net] On Behalf Of strk
>> Sent: 19 février 2010 14:42
>> To: PostGIS Development Discussion
>> Subject: Re: [postgis-devel] [PostGIS] #413: ST_Single_Sided_Buffer added
>>
>> On Fri, Feb 19, 2010 at 01:52:03AM -0200, George Silva wrote:
>>     
>>> I'm sorry to give my 2 cents, but in most softwares everything it's just
>>> called buffer, with different parameters.
>>>       
>> Could you please provide a full call example of a few of these softwares
>> to obtain what the ST_Single_Sided_Buffer would give ?
>> What it does is giving a linestring offsetted from the original
>> (no area returned).
>>
>> --strk;
>>
>>  ()   Free GIS & Flash consultant/developer
>>  /\   http://foo.keybit.net/~strk/services.html
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>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022




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