stat_sf_coordinates()
extracts the coordinates from 'sf' objects and
summarises them to one pair of coordinates (x and y) per geometry. This is
convenient when you draw an sf object as geoms like text and labels (so
geom_sf_text()
and geom_sf_label()
relies on this).
stat_sf_coordinates(
mapping = aes(),
data = NULL,
geom = "point",
position = "identity",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE,
fun.geometry = NULL,
...
)
The data to be displayed in this layer. There are three options:
If NULL
, the default, the data is inherited from the plot
data as specified in the call to ggplot()
.
A data.frame
, or other object, will override the plot
data. All objects will be fortified to produce a data frame. See
fortify()
for which variables will be created.
A function
will be called with a single argument,
the plot data. The return value must be a data.frame
, and
will be used as the layer data. A function
can be created
from a formula
(e.g. ~ head(.x, 10)
).
The geometric object to use display the data
Position adjustment, either as a string, or the result of a call to a position adjustment function.
If FALSE
, the default, missing values are removed with
a warning. If TRUE
, missing values are silently removed.
logical. Should this layer be included in the legends?
NA
, the default, includes if any aesthetics are mapped.
FALSE
never includes, and TRUE
always includes.
It can also be a named logical vector to finely select the aesthetics to
display.
If FALSE
, overrides the default aesthetics,
rather than combining with them. This is most useful for helper functions
that define both data and aesthetics and shouldn't inherit behaviour from
the default plot specification, e.g. borders()
.
A function that takes a sfc
object and returns a sfc_POINT
with the
same length as the input. If NULL
, function(x) sf::st_point_on_surface(sf::st_zm(x))
will be used. Note that the function may warn about the incorrectness of
the result if the data is not projected, but you can ignore this except
when you really care about the exact locations.
Other arguments passed on to layer()
. These are
often aesthetics, used to set an aesthetic to a fixed value, like
colour = "red"
or size = 3
. They may also be parameters
to the paired geom/stat.
X dimension of the simple feature
Y dimension of the simple feature
coordinates of an sf
object can be retrieved by sf::st_coordinates()
.
But, we cannot simply use sf::st_coordinates()
because, whereas text and
labels require exactly one coordinate per geometry, it returns multiple ones
for a polygon or a line. Thus, these two steps are needed:
Choose one point per geometry by some function like sf::st_centroid()
or sf::st_point_on_surface()
.
Retrieve coordinates from the points by sf::st_coordinates()
.
For the first step, you can use an arbitrary function via fun.geometry
.
By default, function(x) sf::st_point_on_surface(sf::st_zm(x))
is used;
sf::st_point_on_surface()
seems more appropriate than sf::st_centroid()
since lables and text usually are intended to be put within the polygon or
the line. sf::st_zm()
is needed to drop Z and M dimension beforehand,
otherwise sf::st_point_on_surface()
may fail when the geometries have M
dimension.
# NOT RUN {
if (requireNamespace("sf", quietly = TRUE)) {
nc <- sf::st_read(system.file("shape/nc.shp", package="sf"))
ggplot(nc) +
stat_sf_coordinates()
ggplot(nc) +
geom_errorbarh(
aes(geometry = geometry,
xmin = after_stat(x) - 0.1,
xmax = after_stat(x) + 0.1,
y = after_stat(y),
height = 0.04),
stat = "sf_coordinates"
)
}
# }
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