[postgis-users] How to generalize or simplify a Polygon

[Matt Lynch]

Hi Christoph,

I searched the postings with D-P Algorithm and found the posting on Line
Simplification that you mentioned.  I will look into that as it would
ideal for me to have it within PostGIS.

Does anyone have any more details on the self-intersection problem that
was mentioned earlier in the thread?  I haven't been able to come up
with a case where I could see a self-intersection generated.

Thanks,

Matt

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Christoph Spoerri
Sent: Thursday, August 28, 2003 3:06 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] How to generalize or simplify a Polygon


I'm not sure if this was mentioned before, but earlier this summer their
was a 
post on the list by somebody that implemented the D-P algorithm on lines
as 
an extension/function to PostGIS. This may be a good starting point to
also 
simplify polygons (if required).

Along this line, I was also think if it would be possible/useful to
store the 
simplified feature within the database. This would then allow the user
to 
specify which 'version' of a spatial dataset should be retrieved. This
would 
provide a similar functionality as is already available for raster
datasets 
where pyramids are used to provide this functionality. What does the
rest of 
you think about this?

Christoph


On Thursday 28 August 2003 04:29 pm, Martin Davis wrote:
> > of self-intersection when you process a polygon. So why not put it 
> > in as an method that is only a member of LineString / 
> > MultiLineString class ?
>
> If we were putting D-P into JTS, that would be one place to put it, 
> alright.  However, as I said I'd really rather keep JTS focussed on 
> core algorithms.
>
> On a philosophical note, adding algorithms as methods to Geometry 
> objects seems to be encouraged by the OO paradigm, but it's not the 
> most scalable or flexible way of doing things.  For algorithms such as

> D-P which are pretty independent of the internal representation of the

> Geometry I think it's nicer to keep them outside the Geometry class in

> a separate algorithm class.
>
> Martin Davis, Senior Technical Architect
> Vivid Solutions Inc.
> Suite #1A-2328 Government Street   Victoria, B.C.   V8T 5G5
> Phone: (250) 385 6040    Fax: (250) 385 6046
> EMail: mbdavis at vividsolutions.com  Web: www.vividsolutions.com
>


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