snap_sites {rdwplus}

A function to snap survey sites to a stream raster and a flow accumulation raster

Description

This function takes a set of survey site locations and snaps them to the highest-value cell within a flow accumulation raster, within a specified distance. Note that this function calls r.stream.snap, which is a GRASS GIS add-on. It can be installed through the GRASS GUI.

Usage

snap_sites(
  sites,
  stream,
  flow_acc,
  max_move,
  out,
  overwrite = FALSE,
  max_memory = 300,
  ...
)

Arguments

sites

File name for a shapefile containing the locations of the survey sites in the current GRASS mapset.

stream

Name of a stream raster in the current GRASS mapset. This can either be formatted to have NoData in non-stream cells or 0s in non-stream cells.

flow_acc

Name of a flow accumulation raster in the current GRASS mapset.

max_move

The maximum distance in cells that any site can be moved to snap it to the flow accumulation grid.

out

Name of the output in the current GRASS mapset. Note that this function will add a column called snap_dist to the attribute table of the input sites, which indicates how far each site was snapped.

overwrite

Whether the output should be allowed to overwrite any existing files. Defaults to FALSE.

max_memory

Max memory (in) used in memory swap mode. Defaults to 300 Mb.

...

Additional arguments to r.stream.snap.

Value

Nothing.

Examples

# Will only run if GRASS is running
# You should load rdwplus and initialise GRASS via the initGRASS function
if(check_running()){
# Retrieve paths to data sets
dem <- system.file("extdata", "dem.tif", package = "rdwplus")
lus <- system.file("extdata", "landuse.tif", package = "rdwplus")
sts <- system.file("extdata", "site.shp", package = "rdwplus")
stm <- system.file("extdata", "streams.shp", package = "rdwplus")

# Set environment 
set_envir(dem)

# Get other data sets (stream layer, sites, land use, etc.)
raster_to_mapset(lus)
vector_to_mapset(c(stm, sts))

# Reclassify streams
out_stream <- paste0(tempdir(), "/streams.tif")
rasterise_stream("streams", out_stream, TRUE)
reclassify_streams("streams.tif", "streams01.tif", overwrite = TRUE)

# Burn in the streams to the DEM
burn_in("dem.tif", "streams01.tif", "burndem.tif", overwrite = TRUE)

# Fill dem
fill_sinks("burndem.tif", "filldem.tif", "fd1.tif", "sinks.tif", overwrite = TRUE)

# Derive flow direction and accumulation grids
derive_flow("dem.tif", "fd.tif", "fa.tif", overwrite = T)

# Derive a new stream raster from the FA grid
derive_streams("dem.tif", "fa.tif", "new_stm.tif", "new_stm", min_acc = 200, overwrite = T)

# Snap sites to streams and flow accumulation
snap_sites("site", "new_stm.tif", "fa.tif", 2, "snapsite", T)
}