r.lake(1)

1r.lake(1)                     Grass User's Manual                    r.lake(1)
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NAME

6       r.lake  - Fills lake from seed at given level
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KEYWORDS

9       raster
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SYNOPSIS

12       r.lake
13       r.lake help
14       r.lake   [-no]   dem=name   wl=float    [lake=name]     [xy=east,north]
15       [seed=name]   [--overwrite]
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17   Flags:
18       -n  Use negative depth values for lake raster map
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20       -o  Overwrite seed map with result (lake) map
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22       --overwrite
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24   Parameters:
25       dem=name
26           Terrain raster map (DEM)
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28       wl=float
29           Water level
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31       lake=name
32           Output raster map with lake
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34       xy=east,north
35           Seed point coordinates
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37       seed=name
38           Raster map with seed (at least 1 cell > 0)
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DESCRIPTION

41       The module fills a lake to a target water  level  from  a  given  start
42       point.  The  user  can think of it as r.grow with additional checks for
43       elevation.  The resulting raster map contains cells with values  repre‐
44       senting lake depth and NULL for all other cells beyond the lake.
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46       This  module  uses  a 3x3 moving window approach to find all cells that
47       match three criteria and to define the lake:
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49                     cells are below  the  specified  elevation  (i.e.,  water
50                     level);
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52                     cells  are  connected  with  an initial cell (seed or E,N
53                     value);
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55                     cells are not NULL or masked.
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57       The water level must be in DEM units.
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59       The seed (starting) point can be a raster map with at  least  one  cell
60       value  greater  than  zero, or a seed point can be specified as an E, N
61       coordinate pair. If the seed is specified  as  a  coordinate  pair,  an
62       additional  check  is  done to make sure that the target water level is
63       above the level of the DEM. When a raster map is used as a  seed,  how‐
64       ever,  no  such checks are done.  Specifying a target water level below
65       surface represented by DEM will result in an empty map. Note: a  raster
66       lake map created in a previous run can also be used as a seed map for a
67       new run to simulate rising water levels.
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69       The module will create a new map (lake=foo) or can be  set  to  replace
70       the  input  (seed=bar) map if the -o flag is used.  The user can use -o
71       flag to create animations of rising water  level  without  producing  a
72       separate  map  for  each frame.  An initial seed map must be created to
73       start the sequence, and will be overwritten during subsequent runs with
74       resulting  water levels maps (i.e., a single file serves for both input
75       and output).
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77       Negative output (the -n flag) is useful for visualisations in NVIZ.  It
78       equals the mapcalc's expression "negative = 0 - positive".
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KNOWN BUGS AND LIMITATIONS

81                     The entire map is loaded into RAM.
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83                     The  module  is NOT large file safe. (due to the previous
84                     point)
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86                     A completely negative seed map will not  work!  At  least
87                     one  cell must have a value >0. Output from r.lake -n can
88                     NOT be used as input in the next run.
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MAPCALC EQUIVALENT - FOR GRASS HACKERS

91       This module was initially created as a script using r.mapcalc. This had
92       some  limitations  -  it  was slow and no checks where done to find out
93       required iteration count. The shell script code (using r.mapcalc)  used
94       in the original script is shown below:
95       ${seedmap} = if( ${dem}, \
96       if( if( isnull(${seedmap}),0,${seedmap}>0), ${wlevel}-${dem}, \
97        if( \
98         if(isnull(${seedmap}[-1,0]),0,          ${seedmap}[-1,0]>0         &&
99       ${wlevel}>${dem}) ||\
100         if(isnull(${seedmap}[-1,1]),0,         ${seedmap}[-1,1]>0          &&
101       ${wlevel}>${dem}) ||\
102         if(isnull(${seedmap}[0,1]),       0,       ${seedmap}[0,1]>0       &&
103       ${wlevel}>${dem}) ||\
104         if(isnull(${seedmap}[1,1]),      0,       ${seedmap}[1,1]>0        &&
105       ${wlevel}>${dem}) ||\
106         if(isnull(${seedmap}[1,0]),       0,       ${seedmap}[1,0]>0       &&
107       ${wlevel}>${dem}) ||\
108         if(isnull(${seedmap}[1,-1]),0,         ${seedmap}[1,-1]>0          &&
109       ${wlevel}>${dem}) ||\
110         if(isnull(${seedmap}[0,-1]),0,          ${seedmap}[0,-1]>0         &&
111       ${wlevel}>${dem}) ||\
112         if(isnull(${seedmap}[-1,-1]),0,        ${seedmap}[-1,-1]>0         &&
113       ${wlevel}>${dem}),\
114        ${wlevel}-${dem}, null() )))
115        The ${seedmap} variable is replaced by seed map names, ${dem} with DEM
116       map name, and ${wlevel} with target water level.  To get  single  water
117       level,  this  code block is called with same level numerous times (in a
118       loop) as the lake grows by single cells during single run.
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AUTHOR

124       Maris Nartiss (maris.nartiss gmail.com)
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126       Last changed: $Date: 2006/05/23 16:50:05 $
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128       Full index
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132GRASS 6.2.2                                                          r.lake(1)