Runs an algorithm using 'qgis_process'. See the QGIS docs for a detailed description of the algorithms provided 'out of the box' on QGIS.
Usage
qgis_run_algorithm(
algorithm,
...,
PROJECT_PATH = NULL,
ELLIPSOID = NULL,
.raw_json_input = NULL,
.quiet = TRUE
)
Arguments
- algorithm
A qualified algorithm name (e.g.,
"native:buffer"
) or a path to a QGIS model file.- ...
Named key-value pairs as arguments for the algorithm. Features of
rlang::list2()
are supported. These arguments are converted to strings usingas_qgis_argument()
.- PROJECT_PATH, ELLIPSOID
Global values for QGIS project file and ellipsoid name for distance calculations.
- .raw_json_input
The raw JSON to use as input in place of
...
.- .quiet
Use
FALSE
to get extra output from 'qgis_process'. This can be useful in debugging.
Details
qgis_run_algorithm()
accepts various R objects as algorithm arguments.
Examples include an R matrix or data frame for the
argument type 'matrix', R colors for the argument type 'color',
sf or terra (SpatVector) objects for the argument type 'vector' and
raster/terra/stars objects for the argument type 'raster', but there are many
more.
qgis_run_algorithm()
preprocesses the provided objects into the format that
QGIS expects for a given argument.
For data objects in R that already exist as a stored file, it is best to instead provide the file path in order to prevent a superfluous file writing step from R, as QGIS expects a file path. However terra and stars objects can contain the file path as metadata: in these cases this path is retrieved from the R object and passed to QGIS; potential pitfalls are taken care of.
Providing R objects that cannot be converted to the applicable argument type will lead to an error.
Running QGIS models and Python scripts
QGIS models and Python scripts can be added to the Processing Toolbox in the
QGIS GUI, by pointing at their corresponding file.
This will put the model or script below the provider 'Models' or
'Scripts', respectively.
Next, it is necessary to run qgis_configure()
in R in order to make the
model or script available to qgisprocess (even reloading the package won't
detect it, since these providers have dynamic content, not tied to a
plugin or to a QGIS version).
You can check the outcome with qgis_providers()
and
qgis_search_algorithms()
.
Now, just as with other algorithms, you can provide the model:<name>
or
script:<name>
identifier to the algorithm
argument of
qgis_run_algorithm()
.
As the output argument name of a QGIS model can have an R-unfriendly
syntax, you may need to take the JSON parameter string from the QGIS
processing dialog and feed the JSON string to the .raw_json_input
argument
of qgis_run_algorithm()
instead of providing separate arguments.
Although the 'qgis_process' backend also supports replacing the 'algorithm' parameter by the file path of a model file or a Python script, it is not planned to implement this in qgisprocess, as it would bypass argument preprocessing in R (including checks).
See also
Other functions to run one geoprocessing algorithm:
qgis_run_algorithm_p()
Examples
qgis_run_algorithm(
"native:buffer",
INPUT = system.file("longlake/longlake_depth.gpkg", package = "qgisprocess"),
DISTANCE = 10
)
#> Argument `SEGMENTS` is unspecified (using QGIS default value).
#> Using `END_CAP_STYLE = "Round"`
#> Using `JOIN_STYLE = "Round"`
#> Argument `MITER_LIMIT` is unspecified (using QGIS default value).
#> Argument `DISSOLVE` is unspecified (using QGIS default value).
#> Argument `SEPARATE_DISJOINT` is unspecified (using QGIS default value).
#> Using `OUTPUT = qgis_tmp_vector()`
#> <Result of `qgis_run_algorithm("native:buffer", ...)`>
#> List of 1
#> $ OUTPUT: 'qgis_outputVector' chr "/tmp/Rtmpvzg8Cs/file2c8f509e72ff/file2c8f27f4ce0f.gpkg"