No worries, I'm not seeing any differences in the original and the filtered cells. I've tried mode and max methods
Thanks Le gach dea ghui, *Shane Carey* *GIS and Data Solutions Consultant* On Sat, Sep 22, 2018 at 2:39 PM, johannesradinger < johannesradin...@gmail.com> wrote: > Sorry I ment method=mode or median as stated by Markus N. > > > > Sent from my Samsung Galaxy smartphone. > > -------- Original message -------- > From: Shane Carey <careys...@gmail.com> > Date: 22/09/2018 15:05 (GMT+01:00) > To: Johannes Radinger <johannesradin...@gmail.com> > Cc: Markus Neteler <nete...@osgeo.org>, GRASS user list < > grass-user@lists.osgeo.org> > Subject: Re: [GRASS-user] Elevation above a river > > This works a treat - super stuff - thanks Johannes. > > Could you point me in the direction of an algorithim with Grass that can > do the following: > > # Clean some of the spurious cells etc. (using some kind of neighbourhood > filtering) > > Thanks very much > > Le gach dea ghui, > *Shane Carey* > *GIS and Data Solutions Consultant* > > On Sun, Sep 16, 2018 at 8:46 PM, Johannes Radinger < > johannesradin...@gmail.com> wrote: > >> 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. >> >> Here a small example of how the working flow could be using the North >> Caroline example dataset: >> ############## >> # Set region >> g.region raster=elevation@PERMANENT >> >> # Extract elevation of the streams >> r.mapcalc --o expression="streams_elevation = if( >> streams_derived@PERMANENT, elevation@PERMANENT,null())" >> >> # Grow stream_elevation map by a some hundred meters >> r.grow -m --overwrite input=streams_elevation >> output=streams_elevation_grow radius=500 >> >> # Calculate difference between original elevatoin and stream channel >> elevation >> r.mapcalc expression="stream_elevation_diff = elevation@PERMANENT - >> streams_elevation_grow" --overwrite >> >> # Extract areas that are than x meters higher than stream channel >> elevation >> r.mapcalc expression="stream_elevation_diff_smaller1 = if( >> stream_elevation_diff < 1,1,null())" --overwrite >> >> # Maybe here it needs some cleaning of spurious cells etc. (using some >> kind of neighbourhood filtering) >> >> # Raster areas to a vector area (with smoothed corners; s-flag) >> r.to.vect -s --overwrite input=stream_elevation_diff_smaller1 >> output=stream_elevation_diff_smaller1_area type=area >> ############## >> >> HTH >> /Johannes >> >> On Sun, Sep 16, 2018 at 8:53 PM Shane Carey <careys...@gmail.com> wrote: >> >>> Hey Johannes, >>> >>> 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? >>> >>> Thanks >>> >>> On Domh 16 MFómh 2018 at 17:21, Johannes Radinger < >>> johannesradin...@gmail.com> wrote: >>> >>>> 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? >>>> 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. >>>> /Johannes >>>> >>>> On Sun, Sep 16, 2018 at 5:16 PM Markus Neteler <nete...@osgeo.org> >>>> wrote: >>>> >>>>> Hi, >>>>> >>>>> Shane Carey <careys...@gmail.com> schrieb am Fr., 14. Sep. 2018, >>>>> 23:02: >>>>> >>>>>> Hi All, >>>>>> >>>>>> 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. >>>>>> >>>>>> 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. >>>>>> >>>>> >>>>> This isn't clear to me. Could you elaborate? >>>>> >>>>> Best >>>>> Markus >>>>> >>>>> >>>>> Thanks all. >>>>>> >>>>>> Le gach dea ghui, >>>>>> *Shane Carey* >>>>>> *GIS and Data Solutions Consultant* >>>>>> _______________________________________________ >>>>>> grass-user mailing list >>>>>> grass-user@lists.osgeo.org >>>>>> https://lists.osgeo.org/mailman/listinfo/grass-user >>>>> >>>>> _______________________________________________ >>>>> grass-user mailing list >>>>> grass-user@lists.osgeo.org >>>>> https://lists.osgeo.org/mailman/listinfo/grass-user >>>> >>>> -- >>> Le gach dea ghui, >>> *Shane Carey* >>> *GIS and Data Solutions Consultant* >>> >> >
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