[Gdal-dev] Cookie cutting shapefiles in OGR

[Gauthier,Jean-Philippe [CMC]]

	If I may add on the GPC vs GEOS choice, since we used GPC also,

	Some of the processing we did used to take hours up to days
using GEOS and we can now do them in minutes using GPC, GEOS is very
nice and has useful other fonctionnalities but is 2 orders of magnitude
too slow.

	JP

-----Original Message-----
From: gdal-dev-bounces at lists.maptools.org
[mailto:gdal-dev-bounces at lists.maptools.org] On Behalf Of Chapman,
Martin
Sent: 05 July, 2006 12:23
To: Frank Warmerdam
Cc: gdal-dev at lists.maptools.org
Subject: RE: [Gdal-dev] Cookie cutting shapefiles in OGR


Frank,

The reason I use GPC is when I render projected maps that have a central
meridian that != 0 I have to partition the geometries that cross the new
edge of the map.  Also, I provide a clipping utility to clip small
vector sets from large datasets.  You are correct that there is really
no need other than convenience to add GPC to OGR.  I just thought it
would add some nice functionality to OGR without the overhead of GEOS. I
emailed the GPC people and they told me that all that is needed for a
commercial application is a one time donation to use it commercially.
Otherwise it's free of charge.  

Best regards,
Martin 

-----Original Message-----
From: Frank Warmerdam [mailto:fwarmerdam at gmail.com] On Behalf Of Frank
Warmerdam
Sent: Tuesday, July 04, 2006 8:23 PM
To: Chapman, Martin
Cc: Alexandre Leroux; gdal-dev at lists.maptools.org
Subject: Re: [Gdal-dev] Cookie cutting shapefiles in OGR

Chapman, Martin wrote:
  > 2.  If you actually want to clip intersecting geometries and reshape
> them to your cookie cutter geometry then you need to use a library
like
> GPC (http://www.cs.man.ac.uk/~toby/alan/software/ ).  This open source

> library is very simple to use and works great...and it's very fast.
If
> you have problems using it let me know and I will help you out.  If 
> Frank W. is reading this posting I would urge him to consider
including
> GPC as part of OGR since it's small, fast, powerful, and easy to use. 
> LineString and Point clipping is easy and you should be able to find 
> algorithms on-line or come up with one yourself.  GPC also supports 
> difference, intersection, exclusive-or and union clip operations.  The
> C++ code I use for GPC is listed below the java code.

Martin,

What reasons do/did you have to use GPC instead of GEOS?  I can imagine
it is smaller, and faster.  As mentioned earlier GPC isn't open source,
so I would prefer to use GEOS but I wouldn't be opposed to having
optional GPC based implementation of some of the geometry operations if
there was a really substantial advantage to GPC.

Of course, using GPC outside OGR is already quite doable, so my
integration is not required ... at most a convenience.

Best regards,
-- 
---------------------------------------+--------------------------------
------
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    | President OSGF,
http://osgeo.org


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