qgis is automatically generated package which originates from qgisprocess and aims to provide calls and simple documentation for each QGIS functions available in core and the most important algorithm providers (GRASS GIS and Saga). The algorithms are automatically extracted from fresh install of latest QGIS version on Ubuntu with packages for GRASS and SAGA installed.
The package is highly experimental and things are quite likely to change a lot in the future. The definition of individual functions can change if it changes in the QGIS.
Latest package version 3.40.1.9000 is build against QGIS version 3.40.1-Bratislava.
You can install the released version of qgis from GitHub with:
# install.package("remotes")
remotes::install_github("JanCaha/r_package_qgis")
The information about local installation are in a vignette
vignette("local_instalation").
The idea of the package is that it should not be loaded directly using
library(qgis) but rather functions should be called using
qgis::function_name() syntax. Even though tests showed (see them
here)
that loading the package does not takes significant amount of resources.
The author’s suggestion is still to avoid loading and use the
package::function() notation.
The names of the functions follow general pattern of
algorithm-provider_algorithm-id with only the native QGIS
algorithms using qgis algorithm provider instead of native.
The available providers are: 3d, gdal, grass, native, qgis, sagang. The overall number of available algorithms is 1180.
Every functions carries three boolean parameters that allow better
utilization of these functions in R pipelines and reports. These are
.complete_output, .quiet and .messages. The default setting of
these variables is such that the calls are as silent as possible and
create pretty much no output in R console at all.
Parameter .quiet (default values is TRUE) is the same as in
qgisprocess::qgis_run_algorithm() only in qgis the functions are
silent by default while in qgisprocess they are talkative.
Parameter .messages (default value is FALSE) controls if messages
produced by qgisprocess (such as information about parameters not
being set etc.) should be outputed or not.
Parameter .complete_output(default values is TRUE) specifies whether
whole QGIS process output should be returned or only first variable in
it, which is usually the main output.
These three parameters can also be set as R session options using
options(qgis.quiet = TRUE), options(qgis.messages = FALSE) and
options(qgis.complete_output = TRUE) to avoid the need to set them for
every individual function call.
qgis::qgis_buffer()
This allows you to show the help page for the function (at least in RStudio using the key shortcut F1).
This example uses qgisprocess pipe ability to directly load output to
R.
library(sf)
#> Linking to GEOS 3.10.2, GDAL 3.4.1, PROJ 8.2.1; sf_use_s2() is TRUE
nc <- st_read(system.file("shape/nc.shp", package="sf"), quiet = TRUE)
buffered <- qgis::qgis_buffer(INPUT = nc,
DISTANCE = 0.2,
END_CAP_STYLE = "Flat") %>%
st_as_sf()
plot(buffered["NAME"])
