geom_cnt {centerline} | R Documentation |
Plot centerline with ggplot2
Description
Binding for ggplot2::geom_sf()
, therefore it supports
only sf
objects.
Usage
geom_cnt(
mapping = ggplot2::aes(),
data = NULL,
stat = "sf",
position = "identity",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE,
keep = 0.5,
method = c("voronoi", "straight"),
simplify = TRUE,
...
)
Arguments
mapping |
Set of aesthetic mappings created by aes() . If specified and
inherit.aes = TRUE (the default), it is combined with the default mapping
at the top level of the plot. You must supply mapping if there is no plot
mapping.
|
data |
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) ).
|
stat |
The statistical transformation to use on the data for this layer.
When using a geom_*() function to construct a layer, the stat
argument can be used the override the default coupling between geoms and
stats. The stat argument accepts the following:
A Stat ggproto subclass, for example StatCount .
A string naming the stat. To give the stat as a string, strip the
function name of the stat_ prefix. For example, to use stat_count() ,
give the stat as "count" .
For more information and other ways to specify the stat, see the
layer stat documentation.
|
position |
A position adjustment to use on the data for this layer. This
can be used in various ways, including to prevent overplotting and
improving the display. The position argument accepts the following:
The result of calling a position function, such as position_jitter() .
This method allows for passing extra arguments to the position.
A string naming the position adjustment. To give the position as a
string, strip the function name of the position_ prefix. For example,
to use position_jitter() , give the position as "jitter" .
For more information and other ways to specify the position, see the
layer position documentation.
|
na.rm |
If FALSE , the default, missing values are removed with
a warning. If TRUE , missing values are silently removed.
|
show.legend |
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.
You can also set this to one of "polygon", "line", and "point" to
override the default legend.
|
inherit.aes |
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() .
|
keep |
numeric, proportion of points to retain (0.05-5.0; default 0.5).
See Details.
|
method |
character, either "voronoi" (default) or
"straight" , or just the first letter "v" or "s" .
See Details.
|
simplify |
logical, if TRUE (default) then the
centerline will be smoothed with smoothr::smooth_ksmooth()
|
... |
Other arguments passed on to layer() 's params argument. These
arguments broadly fall into one of 4 categories below. Notably, further
arguments to the position argument, or aesthetics that are required
can not be passed through ... . Unknown arguments that are not part
of the 4 categories below are ignored.
Static aesthetics that are not mapped to a scale, but are at a fixed
value and apply to the layer as a whole. For example, colour = "red"
or linewidth = 3 . The geom's documentation has an Aesthetics
section that lists the available options. The 'required' aesthetics
cannot be passed on to the params . Please note that while passing
unmapped aesthetics as vectors is technically possible, the order and
required length is not guaranteed to be parallel to the input data.
When constructing a layer using
a stat_*() function, the ... argument can be used to pass on
parameters to the geom part of the layer. An example of this is
stat_density(geom = "area", outline.type = "both") . The geom's
documentation lists which parameters it can accept.
Inversely, when constructing a layer using a
geom_*() function, the ... argument can be used to pass on parameters
to the stat part of the layer. An example of this is
geom_area(stat = "density", adjust = 0.5) . The stat's documentation
lists which parameters it can accept.
The key_glyph argument of layer() may also be passed on through
... . This can be one of the functions described as
key glyphs, to change the display of the layer in the legend.
|
Value
A Layer
ggproto object that can be added to a plot.
CRS
coord_sf()
ensures that all layers use a common CRS. You can
either specify it using the crs
param, or coord_sf()
will
take it from the first layer that defines a CRS.
Combining sf layers and regular geoms
Most regular geoms, such as geom_point()
, geom_path()
,
geom_text()
, geom_polygon()
etc. will work fine with coord_sf()
. However
when using these geoms, two problems arise. First, what CRS should be used
for the x and y coordinates used by these non-sf geoms? The CRS applied to
non-sf geoms is set by the default_crs
parameter, and it defaults to
NULL
, which means positions for non-sf geoms are interpreted as projected
coordinates in the coordinate system set by the crs
parameter. This setting
allows you complete control over where exactly items are placed on the plot
canvas, but it may require some understanding of how projections work and how
to generate data in projected coordinates. As an alternative, you can set
default_crs = sf::st_crs(4326)
, the World Geodetic System 1984 (WGS84).
This means that x and y positions are interpreted as longitude and latitude,
respectively. You can also specify any other valid CRS as the default CRS for
non-sf geoms.
The second problem that arises for non-sf geoms is how straight lines
should be interpreted in projected space when default_crs
is not set to NULL
.
The approach coord_sf()
takes is to break straight lines into small pieces
(i.e., segmentize them) and then transform the pieces into projected coordinates.
For the default setting where x and y are interpreted as longitude and latitude,
this approach means that horizontal lines follow the parallels and vertical lines
follow the meridians. If you need a different approach to handling straight lines,
then you should manually segmentize and project coordinates and generate the plot
in projected coordinates.
See Also
geom_cnt_text()
, geom_cnt_label()
, ggplot2::geom_sf()
Examples
library(sf)
library(ggplot2)
lake <-
sf::st_read(
system.file("extdata/example.gpkg", package = "centerline"),
layer = "lake",
quiet = TRUE
)
ggplot() +
geom_sf(data = lake) +
geom_cnt(
data = lake,
keep = 1,
simplify = TRUE
) +
theme_void()
[Package
centerline version 0.2.2
Index]