[postgis-users] ST_Simplify

[Kevin Neufeld]

Hi Andy,

Can you post a small example?
-- Kevin


On 10/21/2010 10:02 AM, lplateandy wrote:
> Hi,
>
> I have, in the simplest example, a square polygon of 1 by 1 kilometer size
> with nodes every 25 meters.
>
> I can use ST_Simplify (the_geom,5) to remove most of the points.
>
> However, for some reason i end up with the four corner nodes and a fifth
> node 25m clockwise from the top left corner.
>
> In itself, this would be fine - 5 nodes is better than 160.
>
> However, on some of the polygons, there are more complex boundaries which i
> wish to smooth out using simplify. I would do this with  ST_Simplify
> (the_geom,26) example - going over the minimum 25 metres between  any nodes.
>
> In the example of the square with 5 nodes, the problem i find then is that
> the top left node is removed and the one 25m clockwise remains. The result
> is that i no longer have a 1km square but sloping Western boundary correctly
> going 1km North South but incorrectly veering across 25m to the East.
>
> Is there a way to remove the stray node so i am more likely to maintain my
> overall polygon shape. I did try st_simplifiypreservetopology but saw no
> noticeable difference.
>
> Hope that makes sense, any help much appreciated
>
> Andy