topic Gaining central lines from buffer areas in Geoprocessing Questions

Gaining central lines from buffer areas

MatthiasWoerner — Mon, 03 Dec 2012 19:53:00 GMT

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

Re: Gaining central lines from buffer areas

MichaelKowalczyk — Tue, 04 Dec 2012 11:12:33 GMT

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.

Re: Gaining central lines from buffer areas

DarrenWiens2 — Tue, 04 Dec 2012 20:21:53 GMT

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)

Re: Gaining central lines from buffer areas

DanPatterson_Retired — Wed, 05 Dec 2012 08:06:27 GMT

What you want is the "medial axis". There are no built-in tools to do this other than the proposed workarounds

Re: Gaining central lines from buffer areas

MatthiasWoerner — Fri, 07 Dec 2012 14:30:15 GMT

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

Re: Gaining central lines from buffer areas

markdenil — Fri, 07 Dec 2012 16:22:18 GMT

Perhaps CollapseDualLinesToCenterline_cartography would help.
It is an advanced tool in the Cartography / generalization tool box.