Visualise vector fields (such as, electric/magnetic fields, wind speed, or water currents) with arrows as a layer in a ggplot.
GeomFieldsgeom_fields(
mapping = NULL,
data = NULL,
stat = "fields",
position = "identity",
na.rm = FALSE,
show.legend = NA,
max_radius = ggplot2::unit(0.5, "cm"),
.angle_correction = angle_correction,
arrow = grid::arrow(length = ggplot2::unit(0.2, "cm")),
inherit.aes = TRUE,
...
)
An object of class GeomFields (inherits from GeomSegment, Geom, ggproto, gg) of length 8.
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.
Can be one of four things:
The statistical transformation to use on the data for this layer. By default it is
set to GeomFields() ("fields").
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.
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.
Maximum radius to which the radius aesthetic is scaled in the plot.
You can use absolute ("e.g., "cm", "in", "pt") and relative ("npc") units to set
its value. Default is 0.5 cm.
Function to correct the angle in the aesthetics for the projection and/or
aspect ratio used in the plot. When set to NULL the angle is not corrected and is treated as the angle
in the final plot. A custom function can be provided which should accept at least three arguments
(data, panel_params and coord). See angle_correction() and vignette("angle_correction") for
more details.
specification for arrow heads, as created by grid::arrow().
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().
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.
geometry|x: Either a geometry column or x coordinate.
In case of geometry the column should be of class sf::sfc_POINT.
In case of x, it should be a numeric vector, and the aesthetic
y needs to be specified as well. It specifies the location of
the origin of each vector.
radius: This aesthetic will be used to scale the radius of the
vector arrows in the field you wish to display. The maximum radius of the
arrows is given by parameter max_radius. See vignette("radius_aes") for
more details.
angle: This aesthetic represent the angles of the vectors in your
field in radians. Contrary to the mathematical definition, an angle of 0 radians will
point upwards (instead of to the right). This was chosen such because in most geographical
applications an angle of zero degrees points Northwards. Before plotting these angles are
corrected by the function passed to the .angle_correction argument.
See vignette("angle_corrections) for more details.
y: This aesthetic needs to be used in combination with the x aesthetic.
It needs to be a numeric vector.
fill: See vignette("ggplot2-specs", "ggplot2")
colour: See vignette("ggplot2-specs", "ggplot2")
linetype: See vignette("ggplot2-specs", "ggplot2")
linewidth: See vignette("ggplot2-specs", "ggplot2")
alpha: A variable to control the opacity of an element.
Pepijn de Vries
Adds a layer with vector fields to a ggplot. In order to achieve this
two special aesthetic are required: radius and angle.
data(seawatervelocity)
if (requireNamespace("ggplot2") && requireNamespace("stars") &&
requireNamespace("scales")) {
library(ggplot2)
library(stars)
sw_df <- as.data.frame(seawatervelocity)
ggplot(sw_df, aes(x = x, y = y, radius = as.numeric(v), angle = as.numeric(angle))) +
geom_fields(max_radius = unit(0.5, "cm"), na.rm = TRUE)
ggplot() +
geom_fields(data = seawatervelocity,
mapping = aes(radius = as.numeric(v),
angle = as.numeric(angle),
col = as.numeric(v)),
max_radius = unit(0.5, "cm")) +
scale_colour_viridis_c()
}
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