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* >> >
_______________________________________________ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
