Hi Ben,
What you want are single sided, open buffers - or one could also call it
"ST_Parallel(the_geom,distance)". This doesn't exist yet in Postgis,
though I believe that geos (the underlying geometry engine) already
supports it (at least the single-sided buffer - not sure about the open
buffers).
See
http://geos.osgeo.org/doxygen/classgeos_1_1operation_1_1buffer_1_1BufferBuilder.html
- there is a bufferLineSingleSided function available.
So I believe that the single sided part would be a matter of exposing
the geos functionality in Postgis - the "open buffer" part would be
perhaps more work.
Andreas
On 12/23/2010 04:56 AM, Ben Madin wrote:
Thanks Brent,
Happy Christmas / New Year to you as well!
On 23/12/2010, at 2:07 PM, pcr...@pcreso.com wrote:
ST_Translate() is the simplest, but if your lines are horizontal you may want a
Y shift as well?
http://postgis.refractions.net/documentation/manual-svn/ST_Translate.html
Lines are roads, so they go every which way.
Having done this, I suggest you also use ST_reverse() to reflect the direction
is now going the other way (unless it already is :-)
http://postgis.refractions.net/documentation/manual-svn/ST_Reverse.html
For more complex shifting of features, probably overkill in your case, see
http://postgis.refractions.net/documentation/manual-svn/ST_Affine.html
This might be what I am after, but I was thinking of somehow translating each
segment parallel to it's current alignment and then rejoining with a nice
smooth curve... kind of like a 1-sided buffer.
cheers
Ben
--- On Thu, 12/23/10, Ben Madin<li...@remoteinformation.com.au> wrote:
From: Ben Madin<li...@remoteinformation.com.au>
Subject: [postgis-users] Shifting linestrings left
To: "PostGIS Users Discussion"<postgis-users@postgis.refractions.net>
Date: Thursday, December 23, 2010, 3:13 PM
G'day all,
I have a problem where I am trying to show the route of livestock movements,
but I am loosing information when the travel along the same road in different
directions (ie in some cases they travel from a saleyard to a feedlot, then
back to the saleyard after a period). The roads they travel along are single
linestrings.
Is there a way to 'shift' the linestring to the left - after all, that would be
sensible side of the road to drive on...
cheers
Ben
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