[postgis-users] Move road lines to pavement lines?

[James David Smith]

Hi Hug,

Thanks for your email. I did not realise that the st_offsetcurve
function existed!  It looks like it will do what I would like to do.
However there is a problem. In the documentation for st_offsetcurve
here:

http://postgis.refractions.net/docs/ST_OffsetCurve.html

It says that lines like this are not valid:

http://i.stack.imgur.com/bCUjt.png

However some of the journeys along roads that I want to adjust DO have
this sort of format to the line.
Any ideas?

Thanks

James

On 25 October 2013 17:25, Hugues François <hugues.francois at irstea.fr> wrote:
> Hello,
>
> Did you take a look et st_offsetcurve ? The documentation says: " For positive distance the offset will be at the left side of the input line and retain the same direction."
>
> Hug
>
> James David Smith <james.david.smith at gmail.com> a écrit :
>
> Hi there,
>
> Just looking for some general thoughts and guidance on the best way to
> do this please. What I have is about 50,000 linestrings of varying
> length. They are in a projected coordinate system (OSGB36). They
> represent people walking around a city. The routing however has been
> done as road centrelines. So what I would like to do, is to move each
> line 3 metres to the left so that it gives a better representation of
> where they actually walked. I realise this is very inexact, but it
> will do for my purposes.
>
> So does anyone have any thoughts about how to do this? Obviously
> 'left' is a relative term as it will depend on the direction of
> travel.
>
> I think maybe I need to break apart the linestring into collections of
> two points. XY_start and XY_end. Then calculate the angle between
> them. The add or subtract 3 metres onto one of the sets of coordinates
> in one direction, depending on what the result of the angle
> calculation was. Once I've done this, I could then recombine all the
> sets of points back into linestrings. Does this sound like a
> reasonable approach? (Whether I'll actually be able to do it or not is
> another thing).
>
> Thanks
>
> James
> _______________________________________________
> postgis-users mailing list
> postgis-users at lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
> _______________________________________________
> postgis-users mailing list
> postgis-users at lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users