The new .gpkg file is created in the same directory as the input
.osm.pbf file. The translation process is performed using the
vectortranslate utility in sf::gdal_utils(). This operation can be
customized in several ways modifying the parameters layer, extra_tags,
osmconf_ini, vectortranslate_options, boundary and boundary_type.
The .osm.pbf files processed by GDAL are usually categorized into 5
layers, named points, lines, multilinestrings, multipolygons and
other_relations. Check the first paragraphs
here for more details. This
function can covert only one layer at a time, and the parameter layer is
used to specify which layer of the .osm.pbf file should be converted.
Several layers with different names can be stored in the same .gpkg file.
By default, the function will convert the lines layer (which is the most
common one according to our experience).
The arguments osmconf_ini and extra_tags are used to modify how GDAL
reads and processes a .osm.pbf file. More precisely, several operations
that GDAL performs on the input .osm.pbf file are governed by a CONFIG
file, that can be checked at the following
link.
The basic components of OSM data are called
elements and they are
divided into nodes, ways or relations, so, for example, the code at
line 7 of that file is used to determine which ways are assumed to be
polygons (according to the simple-feature definition of polygon) if they
are closed. Moreover, OSM data is usually described using several
tags, i.e pairs of two items:
a key and a value. The code at lines 33, 53, 85, 103, and 121 is used to
determine, for each layer, which tags should be explicitly reported as
fields (while all the other tags are stored in the other_tags column).
The parameter extra_tags is used to determine which extra tags (i.e.
key/value pairs) should be added to the .gpkg file (other than the
default ones).
By default, the vectortranslate operations are skipped if the function
detects a file having the same path as the input file, .gpkg extension, a
layer with the same name as the parameter layer and all extra_tags. In
that case the function will simply return the path of the .gpkg file.
This behaviour can be overwritten setting force_vectortranslate = TRUE.
The vectortranslate operations are never skipped if osmconf_ini,
vectortranslate_options, boundary or boundary_type arguments are not
NULL.
The parameter osmconf_ini is used to pass your own CONFIG file in case
you need more control over the GDAL operations. Check the package
introductory vignette for an example. If osmconf_ini is equal to NULL
(the default value), then the function uses the standard osmconf.ini file
defined by GDAL (but for the extra tags).
The parameter vectortranslate_options is used to control the options that
are passed to ogr2ogr via sf::gdal_utils() when converting between
.osm.pbf and .gpkg formats. ogr2ogr can perform various operations
during the conversion process, such as spatial filters or SQL queries.
These operations can be tuned using the vectortranslate_options argument.
If NULL (the default value), then vectortranslate_options is set equal
to
c("-f", "GPKG", "-overwrite", "-oo", paste0("CONFIG_FILE=", osmconf_ini), "-lco", "GEOMETRY_NAME=geometry", layer).
Explanation:
"-f", "GPKG" says that the output format is GPKG;
"-overwrite is used to delete an existing layer and recreate
it empty;
"-oo", paste0("CONFIG_FILE=", osmconf_ini) is used to set the
Open Options
for the .osm.pbf file and change the CONFIG file (in case the user
asks for any extra tag or a totally different CONFIG file);
"-lco", "GEOMETRY_NAME=geometry" is used to change the
layer creation options
for the .gpkg file and modify the name of the geometry column;
layer indicates which layer should be converted.
If vectortranslate_options is not NULL, then the options c("-f", "GPKG", "-overwrite", "-oo", "CONFIG_FILE=", path-to-config-file, "-lco", "GEOMETRY_NAME=geometry", layer) are always appended unless the user
explicitly sets different default parameters for the arguments -f, -oo,
-lco, and layer.
The arguments boundary and boundary_type can be used to set up a
spatial filter during the vectortranslate operations (and speed up the
process) using an sf or sfc object (POLYGON or MULTIPOLYGON). The
default arguments create a rectangular spatial filter which selects all
features that intersect the area. Setting boundary_type = "clipsrc" clips
the geometries. In both cases, the appropriate options are automatically
added to the vectortranslate_options (unless a user explicitly sets
different default options). Check Examples in oe_get() and the
introductory vignette.
See also the help page of sf::gdal_utils() and
ogr2ogr for more examples and
extensive documentation on all available options that can be tuned during
the vectortranslate process.