Micha and Achim, thank you for the replies. In response to your questions, I am trying to convert a raster map (a scanned & georeferenced map with only XY data) with a shoreline and some wetland islands into a vector map so I can compare gains/losses over time.
A preview of the map is here: http://historicalcharts.noaa.gov/tiled_jpgs_done/zoomifyURLDrivenWebPage.htm?zoomifyImagePath=579-12-1929 The command I used is as follows: r.thin input=NOAA1929 output=NOAA1929THIN iterations=6000 I have tried r.thin with 1000 iterations, which did successfully thin the lines down to the features borders quite well, however only 50% of the map was completed. I bumped the iterations up to 6000, it completed in 4200, but it seemed that it thinned the entire map down to a 1px line. Thanks --- On Tue, 11/9/10, Micha Silver <[email protected]> wrote: From: Micha Silver <[email protected]> Subject: Re: [GRASS-user] r.thin ? To: "charlie" <[email protected]> Cc: [email protected] Date: Tuesday, November 9, 2010, 5:24 AM charlie wrote: > Hi. I am currently using Grass 6.4 on linux and beginning the the process of > vectorizing an old NOAA raster map with r.thin. The map is approximately > 12,000 pixels by 8,000 pixels wide. > > According to this post, ( > http://osgeo-org.1803224.n2.nabble.com/r-thin-td2718260.html#a2718260 )the > iteration variable has to be equal or larger than half the number of cells of > the wider line so I increased the iterations to 6,000, and it would up finishing in approximately 4,200 passes. > > Previously, I was getting excellent preliminary results, with fewer (1,000) > iterations, distinct features were visible, however at least 50% of the map > was not completed. > Now with an increase to 6,000 iterations r.thin completes, but the results > are a single 1px wide horizontal line. Im sure I am overlooking something > relatively simple; can anyone give me any advice on how to best run r.thin in > this particular case? > What is it you are trying to do? The r.thin module is designed to make line features in a raster exactly one pixel wide so that when converting to a line vector, the line will be clean. If you run r.thin on a raster that represents areas, and give a high enough iteration value, the areas will eventually be reduced to lines. > > Thanks! > > Charlie > > > <a href="http://www.wetlandresearch.com";>Wetlands</a> > > > This mail was received via Mail-SeCure System. > ------------------------------------------------------------------------ > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user > > This mail was received via Mail-SeCure System. > > >
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