r.lake(1grass) GRASS GIS User's Manual r.lake(1grass)
NAME
r.lake - Fills lake at given point to given level.
KEYWORDS
raster, hydrology, hazard, flood
SYNOPSIS
r.lake
r.lake --help
r.lake [-no] elevation=name water_level=float [lake=name] [coordi-
nates=east,north] [seed=name] [--overwrite] [--help] [--verbose]
[--quiet] [--ui]
Flags:
-n
Use negative depth values for lake raster map
-o
Overwrite seed map with result (lake) map
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
elevation=name [required]
Name of input elevation raster map
water_level=float [required]
Water level
lake=name
Name for output raster map
coordinates=east,north
Seed point coordinates
Either this coordinates pair or a seed map have to be specified
seed=name
Input raster map with given starting point(s) (at least 1 cell > 0)
Either this parameter or a coordinates pair have to be specified
DESCRIPTION
The module fills a lake to a target water level from a given start
point. The user can think of it as r.grow with additional checks for
elevation. The resulting raster map contains cells with values repre-
senting lake depth and NULL for all other cells beyond the lake. Lake
depth is reported relative to specified water level (specified level =
0 depth).
This module uses a 3x3 moving window approach to find all cells that
match three criteria and to define the lake:
• cells are below the specified elevation (i.e., water level);
• cells are connected with an initial cell (seed or coordinates
pair value);
• cells are not NULL or masked.
The water level must be in DEM units.
NOTES
The seed (starting) point can be a raster map with at least one cell
value greater than zero, or a seed point can be specified as an E, N
coordinate pair. If the seed is specified as a coordinate pair, an ad-
ditional check is done to make sure that the target water level is
above the level of the DEM. When a raster map is used as a seed, how-
ever, no such checks are done. Specifying a target water level below
surface represented by DEM will result in an empty map. Note: a raster
lake map created in a previous run can also be used as a seed map for a
new run to simulate rising water levels.
The module will create a new map (lake=foo) or can be set to replace
the input (seed=bar) map if the -o flag is used. The user can use -o
flag to create animations of rising water level without producing a
separate map for each frame. An initial seed map must be created to
start the sequence, and will be overwritten during subsequent runs with
resulting water levels maps (i.e., a single file serves for both input
and output).
Negative output (the -n flag) is useful for visualisations in NVIZ. It
equals the mapcalc’s expression "negative = 0 - positive".
r.mapcalc equivalent - for GRASS hackers
This module was initially created as a script using r.mapcalc. This
had some limitations - it was slow and no checks where done to find out
required iteration count. The shell script code (using r.mapcalc) used
in the original script is shown below:
${seedmap} = if( ${dem}, \
if( if( isnull(${seedmap}),0,${seedmap}>0), ${wlevel}-${dem}, \
if( \
if(isnull(${seedmap}[-1,0]),0, ${seedmap}[-1,0]>0 && ${wlevel}>${dem}) ||\
if(isnull(${seedmap}[-1,1]),0, ${seedmap}[-1,1]>0 && ${wlevel}>${dem}) ||\
if(isnull(${seedmap}[0,1]), 0, ${seedmap}[0,1]>0 && ${wlevel}>${dem}) ||\
if(isnull(${seedmap}[1,1]), 0, ${seedmap}[1,1]>0 && ${wlevel}>${dem}) ||\
if(isnull(${seedmap}[1,0]), 0, ${seedmap}[1,0]>0 && ${wlevel}>${dem}) ||\
if(isnull(${seedmap}[1,-1]),0, ${seedmap}[1,-1]>0 && ${wlevel}>${dem}) ||\
if(isnull(${seedmap}[0,-1]),0, ${seedmap}[0,-1]>0 && ${wlevel}>${dem}) ||\
if(isnull(${seedmap}[-1,-1]),0, ${seedmap}[-1,-1]>0 && ${wlevel}>${dem}),\
${wlevel}-${dem}, null() )))
The ${seedmap} variable is replaced by seed map names, ${dem} with DEM
map name, and ${wlevel} with target water level. To get single water
level, this code block is called with same level numerous times (in a
loop) as the lake grows by single cells during single run.
KNOWN ISSUES
• The entire map is loaded into RAM.
• A completely negative seed map will not work! At least one cell
must have a value > 0. Output from r.lake -n cannot be used as
input in the next run.
EXAMPLE
Example of small flooding along a street (North Carolina sample
dataset):
g.region raster=elev_lid792_1m -p
# water accumulation next to street dam
r.lake elev_lid792_1m coordinates=638759.3,220264.1 water_level=113.4 lake=flooding
# draw resulting lake map over shaded terrain map
r.relief input=elev_lid792_1m output=elev_lid792_1m_shade
d.rast elev_lid792_1m_shade
d.rast flooding
d.vect streets_wake
Small flooding along a street (r.lake, using Lidar 1m DEM)
SEE ALSO
r.mapcalc, r.grow, r.plane
AUTHOR
Maris Nartiss (maris.nartiss gmail.com)
SOURCE CODE
Available at: r.lake source code (history)
Accessed: unknown
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GRASS 7.8.7 r.lake(1grass)
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