[Gdal-dev] downsampling shapefiles ?

[Chapman, Martin]

I agree.  It would be nice to be able to render fewer points when my map
is zoomed way out.  I think arcmap does that kind of thing.  How does a
geometry simplification algorithm work?  Does it look for linear
patterns in the geometry and then somehow eliminate points based on some
sort of angle/distance tolerance?

Martin

-----Original Message-----
From: gdal-dev-bounces at lists.maptools.org
[mailto:gdal-dev-bounces at lists.maptools.org] On Behalf Of Frank
Warmerdam
Sent: Friday, September 09, 2005 8:16 PM
To: Christian G. Tveen
Cc: gdal-dev at lists.maptools.org
Subject: Re: [Gdal-dev] downsampling shapefiles ?


On 9/9/05, Christian G. Tveen <cgt at navicon.dk> wrote:
> Hi,
> 
> I have a number of very fine grained shape files. Is it possible to 
> have gdal in some way downsample these files to be more usable for 
> overview purposes ?

Christian, 

No, there is no support for geometric simplification in OGR.  I just
checked GEOS's API documentation and I don't see anything there either.
I think I have heard there is something in PostGIS for generalization
but I didn't check into it. 

I do think a "textbook" geometry simplification algorithm would be an
asset to GEOS, and I would be willing to expose it in some fashion
through ogr if it were available. 

Best regards,
-- 
---------------------------------------+--------------------------------
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I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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