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.
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.
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)
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.