<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"></head><body><div>Sorry I ment method=mode or median as stated by Markus N.</div><div><br></div><div><br></div><div><br></div><div id="composer_signature"><div style="font-size:85%;color:#575757" dir="auto">Sent from my Samsung Galaxy smartphone.</div></div><div><br></div><div style="font-size:100%;color:#000000"><!-- originalMessage --><div>-------- Original message --------</div><div>From: Shane Carey <careyshan@gmail.com> </div><div>Date: 22/09/2018 15:05 (GMT+01:00) </div><div>To: Johannes Radinger <johannesradinger@gmail.com> </div><div>Cc: Markus Neteler <neteler@osgeo.org>, GRASS user list <grass-user@lists.osgeo.org> </div><div>Subject: Re: [GRASS-user] Elevation above a river </div><div><br></div></div><div dir="ltr"><div>This works a treat - super stuff - thanks Johannes.</div><div><br></div><div>Could you point me in the direction of an algorithim with Grass that can do the following:</div><div><br></div><div># Clean some of the spurious cells etc. (using some kind of neighbourhood filtering)</div><div><br></div><div>Thanks very much<br></div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div>Le gach dea ghui,<br></div><div><span style="color:rgb(61,133,198)"><b><span style="background-color:rgb(255,255,255)"><i>Shane Carey</i></span></b></span></div><div><span style="color:rgb(61,133,198)"><b><span style="background-color:rgb(255,255,255)"><i>GIS and Data Solutions Consultant</i></span></b></span><br></div></div></div></div></div></div></div></div>
<br><div class="gmail_quote">On Sun, Sep 16, 2018 at 8:46 PM, Johannes Radinger <span dir="ltr"><<a href="mailto:johannesradinger@gmail.com" target="_blank">johannesradinger@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div dir="ltr">That is were the third step should follow, i.e. using r.mapcalc to identify all the cells that are 1m higher than the grown river (irrespective in which distance from the river these cells are located). The rasterized area could then be translated into a vector format using r.to.vect.<div><br></div><div>Here a small example of how the working flow could be using the North Caroline example dataset:</div><div>##############</div><div><div># Set region</div><div>g.region raster=elevation@PERMANENT</div><div><br></div><div># Extract elevation of the streams</div><div>r.mapcalc --o expression="streams_elevation = if( streams_derived@PERMANENT, elevation@PERMANENT,null())"</div><div><br></div><div># Grow stream_elevation map by a some hundred meters</div><div>r.grow -m --overwrite input=streams_elevation output=streams_elevation_grow radius=500</div><div><br></div><div># Calculate difference between original elevatoin and stream channel elevation</div><div>r.mapcalc expression="stream_elevation_<wbr>diff = elevation@PERMANENT - streams_elevation_grow" --overwrite</div><div><br></div><div># Extract areas that are than x meters higher than stream channel elevation</div><div>r.mapcalc expression="stream_elevation_<wbr>diff_smaller1 = if( stream_elevation_diff < 1,1,null())" --overwrite</div><div><br></div><div># Maybe here it needs some cleaning of spurious cells etc. (using some kind of neighbourhood filtering)</div><div><br></div><div># Raster areas to a vector area (with smoothed corners; s-flag)</div><div>r.to.vect -s --overwrite input=stream_elevation_diff_<wbr>smaller1 output=stream_elevation_diff_<wbr>smaller1_area type=area</div><div><div>##############</div><div><br class="m_-1481232220501962477gmail-Apple-interchange-newline"></div></div><div>HTH</div><span class="HOEnZb"><font color="#888888"><div>/Johannes</div></font></span></div></div></div><div class="HOEnZb"><div class="h5"><br><div class="gmail_quote"><div dir="ltr">On Sun, Sep 16, 2018 at 8:53 PM Shane Carey <<a href="mailto:careyshan@gmail.com" target="_blank">careyshan@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div dir="auto">Hey Johannes,</div><div dir="auto"><br></div><div dir="auto">Thanks for your reply. How does r.grow work if let's say the height above the river reaches 1m at 3meters away from the river. And in an other area it reaches the 1meter height at 2meters away from the river. Is it able to follow that line?</div><div dir="auto"><br></div><div dir="auto">Thanks</div><br><div class="gmail_quote"><div>On Domh 16 MFómh 2018 at 17:21, Johannes Radinger <<a href="mailto:johannesradinger@gmail.com" target="_blank">johannesradinger@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>To me this looks like a flooding-related question, i.e. to extract the shore lines of a river if it's water level is raised by 1m or 3m?<div>Maybe (1) extract the raster cells of the elevation map that represents the river channel, (2) then apply r.grow and (3) then r.mapcalc to subtract the grown river channel from the original elevation map. </div></div><div><div>/Johannes</div></div><br><div class="gmail_quote"><div>On Sun, Sep 16, 2018 at 5:16 PM Markus Neteler <<a href="mailto:neteler@osgeo.org" target="_blank">neteler@osgeo.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div>Hi,<br><br><div class="gmail_quote"><div>Shane Carey <<a href="mailto:careyshan@gmail.com" rel="noreferrer" target="_blank">careyshan@gmail.com</a>> schrieb am Fr., 14. Sep. 2018, 23:02:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div>Hi All,</div><div><br></div><div>Does anyone know is it possible to calculate the elevation above a river channel (actual river network that was digitised as opposed to being extracted from a DTM) from a DTM and create a polygon from it. <br></div><div><br></div><div>I need to calculate heights of 1m and 3m above a river channel on both sides of the channel and create a polygon from it.</div></div></blockquote></div></div><div dir="auto"><br></div><div dir="auto">This isn't clear to me. Could you elaborate?</div><div dir="auto"><br></div><div dir="auto">Best</div><div dir="auto">Markus</div><div dir="auto"><br></div><div dir="auto"><br></div><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div>Thanks all.<br></div><div><br></div><div><div><div class="m_-1481232220501962477m_6325447252659228361m_-8945900907715443022m_6169360278670167338m_2339673023995376465m_-8196890261203296796gmail_signature" data-smartmail="gmail_signature"><div><div><div><div><div><div>Le gach dea ghui,<br></div><div><span style="color:rgb(61,133,198)"><b><span style="background-color:rgb(255,255,255)"><i>Shane Carey</i></span></b></span></div><div><span style="color:rgb(61,133,198)"><b><span style="background-color:rgb(255,255,255)"><i>GIS and Data Solutions Consultant</i></span></b></span><br></div></div></div></div></div></div></div></div>
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</blockquote></div></div><div dir="ltr">-- <br></div><div class="m_-1481232220501962477m_6325447252659228361gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div>Le gach dea ghui,<br></div><div><span style="color:rgb(61,133,198)"><b><span style="background-color:rgb(255,255,255)"><i>Shane Carey</i></span></b></span></div><div><span style="color:rgb(61,133,198)"><b><span style="background-color:rgb(255,255,255)"><i>GIS and Data Solutions Consultant</i></span></b></span><br></div></div></div></div></div></div></div>
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