[Gdal-dev] Contouring that outputs polygons?

[Simpson]

I think the vertices of the linestring are drawn through the center of the
pixels on the perimeter of areas of like colored pixels.  In my limited
experience, if the area you are contouring is a straight line of 2 or more
pixels, it is difficult to convert to a polygon.  The buffer function
(available in Postgis) may do it, but I think you'd end up with a larger
representation of the original.

Drew.

-----Original Message-----
From: gdal-dev-bounces at xserve.flids.com
[mailto:gdal-dev-bounces at xserve.flids.com]On Behalf Of Ethan Alpert
Sent: Tuesday, May 24, 2005 1:15 PM
To: Chapman, Martin; gdal-dev
Subject: RE: [Gdal-dev] Contouring that outputs polygons?



Hmm...I'll look into that but I don't think the contour lines can be
closed. On potential problem are boundary conditions. There is no
guarentee given all topologies and subsets that lines can be closed into
polygons.

-e

-----Original Message-----
From: Chapman, Martin [mailto:MChapman at sanz.com]
Sent: Tuesday, May 24, 2005 12:05 PM
To: Ethan Alpert; gdal-dev
Subject: RE: [Gdal-dev] Contouring that outputs polygons?


Ethan,

It might be a hack, but, you could always modify the output by adding
the first point as the last and changing the geometry type to polygon.
Or, you could just mod the gdal_contour code to make a polygon instead
of a linestring.

Just a thought.

Martin

-----Original Message-----
From: gdal-dev-bounces at xserve.flids.com
[mailto:gdal-dev-bounces at xserve.flids.com] On Behalf Of Ethan Alpert
Sent: Tuesday, May 24, 2005 11:43 AM
To: gdal-dev
Subject: [Gdal-dev] Contouring that outputs polygons?




Been looking at gdal_contour a bit and noticed that it's output
shapetype is PolyLine. Does anyone know of any contouring utilities that
will output polygons? I'm not particular about what format but most
contouring apps I've found will render the polygons as images but not
export them.

Thanks,

-e
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