[postgis-users] Map Simplification Program howto use it or is it exist any better alternative?

[Chris Hermansen]

You are correct when you note that two lines that are coincident prior 
to application of DP are unlikely to be coincident afterward.  The 
polygons of which they are part may have gaps and overlaps introduced.

You could avoid this issue by extracting the polygon boundary lines, 
union-ing them together, simplify-ing those, and building back into 
polygons.

Maciej Sawicki wrote:
> Hi,
> I want to simplify complex shp file. I will probably use something
> like DP algorithm
> (http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm). But
> when using DP algorithm for different points sets, common points can
> be treated differently and this causes empty space between polygons.
> To avoid this I need to use algorithm separately for different
> sections.
>
> I tried do it my self with help of geotools but I stumbled into this
> project: http://www.cartoweb.org/downloads/vertexsimplification/documentation.html.
> Unfortunately I don't have much experience with relational databases
> and I don't heave any expedience with postgis.
>
> I tried to simplify this shp:
> http://efele.net/maps/tz/world/tz_world.zip. I installed postgis and
> imported my shp. This is my db:
>
>  Schema |         Name         |   Type   | Owner
> --------+----------------------+----------+--------
>  public | geometry_columns     | table    | viroos
>  public | spatial_ref_sys      | table    | viroos
>  public | tz_world_org         | table    | viroos
>  public | tz_world_org_gid_seq | sequence | viroos
>
> I use this command: python vertex.py -H localhost -u viroos -p
> password -d simplify2 -v public -t public.tz_world -i gid -g geom -m
> 100000
>
> but I get this error:
>
> Vertex Table Generation
> Traceback (most recent call last):
>   File "vertex.py", line 393, in <module>
>     main()
>   File "vertex.py", line 380, in main
>     vertex(schemaVertex,tableIn,colGeo,colId,dmin)
>   File "vertex.py", line 46, in vertex
>     populateVertex(vertex,sequence,colId,colGeo,tableIn,dmin)
>   File "vertex.py", line 105, in populateVertex
>     geometryType= s[0][0]
> IndexError: list index out of range
>
>
> I got no idea what I do wrong :(.
>
> I will appreciate any help with this.
> Also if there is exist any better alternative for doing this I would
> like to hear about it.
>
> TIA for help.
>
> Best regards,
> Maciej Sawicki
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>   


-- 
Regards,

Chris Hermansen · chris.hermansen at timberline.ca · skype:clhermansen
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