[postgis-users] Forming a BAND around a linestring

[pcreso at pcreso.com]

I use a custom equal area projection for some large oceanic regions I work in, but depending on the extent of your linestrings, it is likely that the UTM projection for your part of the globe will give a reasonable result, if you are not too near the poles.

You may even find native lat/long gives an acceptabvle result, it all depends on how much precision you need for your purposes.

Given around 110,000m/degree, if you just want a small buffer around the linestring, and whether it is 5m or 15m doesn't matter, you could try buffering with your lat/long data & a distance of 0.0001 degrees, which should be around 10m, depending on your latitude.

--- On Sat, 3/3/12, Ed Linde <edolinde at gmail.com> wrote:

From: Ed Linde <edolinde at gmail.com>
Subject: Re: [postgis-users] Forming a BAND around a linestring
To: pcreso at pcreso.com
Cc: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
Date: Saturday, March 3, 2012, 7:18 AM

Thanks for the tip! Do you recommend a "suitable projection" for the buffer operation that will not produce distorted buffers?

On Fri, Mar 2, 2012 at 7:15 PM,  <pcreso at pcreso.com> wrote:

ST_Buffer(<linestring>, distance)


http://www.postgis.org/docs/ST_Buffer.html


Note that if your data is lat/long (such as EPSG:4326) with units in degrees, then you will get somewhat distorted buffer distances, and a better result by transforming your linestring to a more suitable projection for the buffer operation, then transform it back.


eg:

ST_Transform(ST_Buffer(ST_Transform(<linestring>, SRID), distance),4326)

HTH,

   Brent Wood
--- On Fri, 3/2/12, Ed Linde <edolinde at gmail.com> wrote:


From: Ed Linde <edolinde at gmail.com>
Subject: [postgis-users] Forming a BAND around a linestring

To: "PostGIS
 Users Discussion" <postgis-users at postgis.refractions.net>
Date: Friday, March 2, 2012, 11:17 PM

Hi All,
I have a set of points with (x,y) co-ordinates that belong to a single object ex: a segment in a road network.If we made a LINESTRING that connected these points (x,y), then I would like to have a BAND or RANGE

around the linestring of say 10 meters wide that would probably make it look more like a polygon or some area. How can I achieve this in postgis 2.0? Do I need to use some library like GDAL in order to achieve this?


Cheers,Ed

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