Convert Polygon to a Line

[Robbo]

Hi There,

I have a roads layer in which all my roads are maped as polygons. I
have a new road managemetn application which would work way better if
my roads were all now lines.

I am wondering if anyone knows of a way to create a polyline layer
that would 'draw' and line down the centre of my polygons.

[Carsten Andersen]

The only way I can think of is first converting the polygon layer to
raster (save Window...) and then using some sort of vectorizing tool
to create a centerline, but I don't know the name of a tool, that will
do this... Hope you can use the idea, though.

Regards, Carsten

[Don Guerra]

The road network we use was created by digitizing the road centerlines and
then buffering those centerlines to create a polygon network. For us, the
polygons really just give the maps some visual enhancement.
Is it possible that your roads were created the same way and the centerlines
are hidden below the buffers?? Just a thought.


Don Guerra

[Driver, Greg 9434]

I haven't tried it, but it looks like you could use this tool from
Spatial Projects:

http://www.spatialprojects.com.au/spatialsql_median.htm

The 'median Line' function seems to provide the ability to create
centre-lines from polygons. The tool is free to download, so it might
be worth giving it go.

HTH

Greg Driver

System Administrator
Applications Support
ICT
Surrey Police
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[Robbo]

Hi All,

Thanks for your comments.
Greg, the Spatial SQL tool is just what I needed to do the job :)

Cheers,
Greg Robertson

On Dec 23, 2:39 am, "Driver, Greg 9434"

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[Cox, Stuart TRAN:EX]

You might be able to find the "Medial Axis" of the polygon that forms the edges of the road segment area and deduce where the likely centerline of the road is/was/might be. I've only an ancient version of MI and can't tell from here what you might be able to obtain from using medial axis' cousin, the voronoi diagram's information, to get you partway there.

Stu Cox
Project Management Technician
Southern Interior Region
Ministry of Transportation and Infrastructure
342-447 Columbia St.,
Kamloops, BC V2C 2T3
p: 250-828-4320
f: 250-828-4229
stuar...@gov.bc.ca

-----Original Message-----
From: mapi...@googlegroups.com [mailto:mapi...@googlegroups.com] On Behalf Of Carsten Andersen
Sent: Monday, December 22, 2008 5:33 AM
To: MapInfo-L
Subject: [MI-L] Re: Convert Polygon to a Line