#Terrain change and topographic analysis using lidar data #Helena Mitasova NCSU #view for the entire region g.region rast=el01.20ft.region -p nviz el01.20ft.region #set region to a smaller area that we will use for practice g.region workshop #compute point density maps for res=3,12 g.region res=3 r.in.xyz lid01small.txt out=lid01.bin.n method=n fs=, x=1 y=2 z=3 #5500 points r.in.xyz lid99small.txt out=lid99.bin.n method=n fs=space x=1 y=2 z=3 #31878 points r.colors lid01.bin.n rast=lid01.bin.n@PERMANENT ^01^99^ d.rast lid01.bin.n d.rast lid99.bin.n #g.region res=9 has still holes so we do 12ft (4m) resolution g.region res=12 r.in.xyz lid01small.txt out=lid01.bin.12ftn method=n fs=, x=1 y=2 z=3 r.in.xyz lid99small.txt out=lid99.bin.12ftn method=n fs=space x=1 y=2 z=3 r.colors lid01.bin.12ftn rast=lid01.bin.n@PERMANENT r.colors lid99.bin.12ftn rast=lid01.bin.n@PERMANENT d.rast lid01.bin.n d.rast lid99.bin.n #compute binned DEM - elevation in each cell is mean elevation of the points within this cell r.in.xyz lid99small.txt out=lid99.bin.12ftmean method=mean fs=space x=1 y=2 z=3 r.slope.aspect lid99.bin.12ftmean zfactor=0.3048 slope=lid99.bin.12slp pcu=lid99.bin.12pc # 12ft (4m) resolution would be sufficient for a general park or community study #but we can get much more detail from the data #import the points (skip topology and dbf, import as 3D point vector if the data set is #too large for topology - over 1mil points) v.in.ascii -ztb lid01small.txt out=lid01pts fs=, z=3 v.in.ascii -ztb lid99small.txt out=lid99pts fs=space z=3 #you can compute surface at higher resolution than your data points - #you won't get more detailed features but you will get better representation #of edges, breaklines, valeys etc. #compute high resolution (3ft~1m) DEM and topographic parameters g.region res=3 v.surf.rst lid99pts elev=lid99.el.def layer=0 slope=lid99.sl.def pcu=lid99.pc.def segmax=20 npmin=100 v.surf.rst lid2001ptss elev=lid01.el.def layer=0 slope=lid01.sl.def pcu=lid01.pc.def segmax=20 npmin=100 #we get high level of detail but for curvatures it is mostly noise d.rast lid99.pc.def d.rast lid01.pc.def #to smoothout the noise and lower LOD we lower tension and increase smoothing v.surf.rst lid99pts elev=lid99.el.t15 layer=0 ten=15 smo=2.0 slope=lid99.sl.t15 pcu=lid99.pc.t15 segmax=20 npmin=100 v.surf.rst lid2001ptss elev=lid01.el.t25 layer=0 ten=25 smo=1.0 slope=lid01.sl.t25 pcu=lid01.pc.t25 segmax=20 npmin=100 #we get better representation of terrain features d.rast lid99.pc.t15 #compare the elevation surfaces in nviz nviz lid99.el.def,lid99.el.t15 #view the entire dune g.region rast=elev99.3ft -p nviz elev99.3ft co=airph98.landcover Appendix color table used for point densities r.colors lid99.bin.12ftn co=rules 0 grey 1 yellow 2 orange 3 red 5 magenta 10 blue 15 cyan 20 green 500 black