Gaining central lines from buffer areas

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12-03-2012 11:53 AM
MatthiasWoerner
New Contributor III
Dear all,

normally buffer polygons are gained from centreal lines. Now I have a file with buffer polygons (of rivers) but actually need the central lines. Is there any chance to gain central lines from the buffer polygons?

Please see the attached screenshot for illustration. To make sure: I don't neet the outlines of the polygons but the central lines, the buffer polygons originally were made of.

Thanks a lot in advance for all hints.

Kind regards,
Matt
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5 Replies
MichaelKowalczyk
New Contributor III
You might try buffering inwards, with a buffer radius equal to half the polygon width.  Then export the narrow "reverse buffer" as a polyline, with a narrow snap tolerance so that you get a single center line. 

I haven't tried this myself, so I can't guarantee that it will work, but hopefully gives you a starting point.
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DarrenWiens2
MVP Honored Contributor
Another method to try is:
1.) Convert buffers to raster (Polygon to Raster - requires ArcInfo/Advanced)
2.) Thin the buffer raster (requires Saptial Analyst)
3.) Convert thinned raster to line (Raster to Polyline)
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DanPatterson_Retired
MVP Esteemed Contributor
What you want is the "medial axis".  There are no built-in tools to do this other than the proposed workarounds
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MatthiasWoerner
New Contributor III
Dear all,

Thanks a lot for all suggestions. I tried the inward buffering, but around the junctions of the river lines there were remaining areas which falsify the line depiction. The result in fact was not better for the planned purpose as before. I suppose it would be the same with the rastering method.

Thanks anyway,
Matt
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markdenil
Regular Contributor II
Perhaps CollapseDualLinesToCenterline_cartography would help.
It is an advanced tool in the Cartography / generalization tool box.
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