<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;"><div id="yiv1699634914"><table id="yiv1699634914bodyDrftID" class="yiv1699634914" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td id="yiv1699634914drftMsgContent" style="font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; font-size-adjust: inherit; font-stretch: inherit; font-family: arial; font-size: 10pt;"><div id="yiv1699634914yiv1442764382"><table id="yiv1699634914yiv1442764382bodyDrftID" class="yiv1699634914yiv1442764382" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td id="yiv1699634914yiv1442764382drftMsgContent" style="font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; font-size-adjust: inherit; font-stretch: inherit; font-family: arial; font-size: 10pt;"><div id="yiv1699634914yiv1442764382yiv1727622015"><table
id="yiv1699634914yiv1442764382yiv1727622015bodyDrftID" class="yiv1699634914yiv1442764382yiv1727622015" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td id="yiv1699634914yiv1442764382yiv1727622015drftMsgContent" style="font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; font-size-adjust: inherit; font-stretch: inherit; font-family: arial; font-size: 10pt;">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.<br><br>A preview of the map is here: http://historicalcharts.noaa.gov/tiled_jpgs_done/zoomifyURLDrivenWebPage.htm?zoomifyImagePath=579-12-1929<br><br>The command I used is as follows:<br>r.thin input=NOAA1929 output=NOAA1929THIN
iterations=6000 <br><br>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.<br><br>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.<br><br>Thanks<br><br>--- On <b>Tue, 11/9/10, Micha Silver
<i><micha@arava.co.il></i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>From: Micha Silver <micha@arava.co.il><br>Subject: Re: [GRASS-user] r.thin ?<br>To: "charlie" <carowan@yahoo.com><br>Cc: grass-user@lists.osgeo.org<br>Date: Tuesday, November 9, 2010, 5:24 AM<br><br><div class="yiv1699634914yiv1442764382yiv1727622015plainMail">charlie wrote:<br><br>> 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.<br>> <br>> According to this post, ( <a rel="nofollow" target="_blank" href="http://osgeo-org.1803224.n2.nabble.com/r-thin-td2718260.html#a2718260">http://osgeo-org.1803224.n2.nabble.com/r-thin-td2718260.html#a2718260</a> )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.<br>> <br>> 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. <br>> 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?<br>> <br><br>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.<br>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.<br><br>> <br>> Thanks!<br>> <br>> Charlie<br>> <br>> <br>> <a
href="http://www.wetlandresearch.com">Wetlands</a><br>> <br>> <br>> This mail was received via Mail-SeCure System.<br>> ------------------------------------------------------------------------<br>> <br>> _______________________________________________<br>> grass-user mailing list<br>> <a rel="nofollow">grass-user@lists.osgeo.org</a><br>> <a rel="nofollow" target="_blank" href="http://lists.osgeo.org/mailman/listinfo/grass-user">http://lists.osgeo.org/mailman/listinfo/grass-user</a><br>> <br>> This mail was received via Mail-SeCure System.<br>> <br>> <br>> <br><br></div></blockquote></td></tr></tbody></table></div></td></tr></tbody></table></div></td></tr></tbody></table></div></td></tr></table>