[postgis-users] gis noob question

[Martin Davis]

You're partly right, Regina.  Simplifypreserve does work on a collection 
basis.  However, it is designed to prevent overlaps from occuring, but 
not "non-overlaps".  So even if you collect the polygons into a 
GeometryCollection, gaps can still occur - this doesn't violate the 
notion of "topology" that is preserved by simplifypreserve.

One way to prevent gaps from happening between coincident linestrings is 
to reduce them to a single linestring. So to simplify a coverage of 
polygons, it should be possible to dissolve them into a single-line 
coverage as a MultiLineString, simplify that, and then polygonize the 
result. 

I haven't tested this, but that's the theory...

Paragon Corporation wrote:
>
> The reason I say no is that that if you collect the geometries first and
> then simplify, I think even simplifypreserve will loop thru each geometry
> anyway and simplify.  Though I'm not absolutely positive of that.  So the
> whole exercise of collect simplify dump is a bit fruitless if that was your
> intention.  Not a bad thought and maybe you are right so maybe someone can
> correct me on that.
>
>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022