[postgis-users] what is the units of distance parameter in the buffer function

[Martin Davis]

The third parameter allows control over the "discretization error" 
during the generation of buffer curves. True buffers contain circular 
arcs, which have to be approximated by a set of line segments. 
Increasing this parameter increases the number of segments used to 
approximate arcs, which (slightly) increases the accuracy of the buffer 
(but makes the result geometry larger).

This parameter doesn't have a huge effect - the default of 8 segments 
per quarter-circle gives only a 1% distance error. It's unlikely you'll 
need more (unless say you want use buffer to generate densified circles).

Pedro Doria Meunier wrote:
>
> Kumar,
>
> If your geom is lat/lon 1=1 degree
>
> As to the 3^rd argument it’s a mystery to me too…
>
> From the manual:
>
> /The optional third parameter sets the number/
>
> /of segment used to approximate a quarter circle (defaults/
>
> /to 8)./
>
> What’s this good for?!
>
> Pedro.
>
> *From:* postgis-users-bounces at postgis.refractions.net 
> [mailto:postgis-users-bounces at postgis.refractions.net] *On Behalf Of 
> *Sandeep Kumar Jakkaraju
> *Sent:* sábado, 2 de Dezembro de 2006 16:38
> *To:* postgis-users at postgis.refractions.net
> *Subject:* [postgis-users] what is the units of distance parameter in 
> the buffer function
>
>
> what is the units of distance parameter in the buffer function ...
>
> buffer(geom,distance,[integer]) ---> buffer(GEOMFROMTEXT('POINT(28.0 
> 79.0)'),1);
>
> if my geom is in lat/lon ..... how much will be 1 !!
>
> can some one throw more light on the 3 rd optional parameter !!! the 
> manual is not clear !!
>
> -- 
> Sandeep Kumar Jakkaraju
> WeBlog:
> http://jakkarajus.blogspot.com <http://jakkarajus.blogspot.com>
>
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022