RQGIS (version 1.0.0)

run_qgis: Interface to QGIS commands

Description

run_qgis calls QGIS algorithms from within R while passing the corresponding function arguments.

Usage

run_qgis(alg = NULL, ..., params = NULL, load_output = FALSE,
  check_params = TRUE, show_msg = TRUE, qgis_env = set_env())

Arguments

alg

Name of the GIS function to be used (see find_algorithms()).

...

Triple dots can be used to specify QGIS geoalgorithm arguments as R named arguments. For more details, please refer to pass_args().

params

Parameter-argument list for a specific geoalgorithm. Please note that you can either specify R named arguments directly via the triple dots (see above) or via a parameter-argument list. However, you may not mix the two methods. See the example section, pass_args() and get_args_man() for more details.

load_output

If TRUE, all QGIS output files (sf::sf()-object in the case of vector data and raster::raster()-object in the case of a raster) specified by the user (i.e. the user has to indicate output files) will be loaded into R. A list will be returned if there is more than one output file (e.g., grass7:r.slope.aspect). See the example section for more details.

check_params

If TRUE (default), it will be checked if all geoalgorithm function arguments were provided in the correct order (deprecated).

show_msg

Logical, if TRUE, Python messages that occurred during the algorithm execution will be shown (deprecated).

qgis_env

Environment containing all the paths to run the QGIS API. For more information, refer to set_env().

Value

The function prints a list (named according to the output parameters) containing the paths to the files created by QGIS. If not otherwise specified, the function saves the QGIS generated output files to a temporary folder (created by QGIS). Optionally, function parameter load_output loads spatial QGIS output (vector and raster data) into R.

Details

This workhorse function calls the QGIS Python API, and specifically processing.runalg.

Examples

# NOT RUN {
# calculate the slope of a DEM
# load dem - a raster object
data(dem, package = "RQGIS")
# find out the name of a GRASS function with which to calculate the slope
find_algorithms(search_term = "grass7.*slope")
# find out how to use the function
alg <- "grass7:r.slope.aspect"
get_usage(alg)
# 1. run QGIS using R named arguments, and load the QGIS output back into R
slope <- run_qgis(alg, elevation = dem, slope = "slope.asc", 
                  load_output = TRUE)
# 2. doing the same with a parameter-argument list
params <- list(elevation = dem, slope = "slope.asc")
slope <- run_qgis(alg, params = params, load_output = TRUE)
# 3. calculate the slope, the aspect and the pcurvature. 
terrain <- run_qgis(alg, elevation = dem, slope = "slope.asc", 
                    aspect = "aspect.asc", pcurvature = "pcurv.asc",
                    load_output = TRUE)
# the three output rasters are returned in a list of length 3
terrain
# }