Help for package ggfields

Title:

Add Vector Field Layers to Ggplots

Version:

0.0.7

Author:

Pepijn de Vries

[aut, cre]

Maintainer:

Pepijn de Vries <pepijn.devries@outlook.com>

Description:

Add vector field layers to ggplots. Ideal for visualising wind speeds, water currents, electric/magnetic fields, etc. Accepts data.frames, simple features (sf), and spatiotemporal arrays (stars) objects as input. Vector fields are depicted as arrows starting at specified locations, and with specified angles and radii.

Depends:

R (≥ 4.1.0)

Imports:

dplyr (≥ 1.1.4), ggplot2 (≥ 3.4.4), grid (≥ 4.1.0), rlang (≥ 1.1.2), sf (≥ 1.0-15), scales (≥ 1.3.0)

Suggests:

CopernicusMarine, knitr, rmarkdown, stars (≥ 0.6-4), testthat (≥ 3.0.0), vdiffr (≥ 1.0.7), svglite (≥ 2.1.3)

License:

GPL (≥ 3)

URL:

https://pepijn-devries.github.io/ggfields/, https://github.com/pepijn-devries/ggfields/

Encoding:

UTF-8

RoxygenNote:

7.2.3

Collate:

'angle_correction.r' 'helpers.r' 'stat_fields.r' 'draw_key_fields.r' 'geom_fields.r' 'annotation_fields.r' 'data.r' 'ggfields-package.r' 'import.r' 'pythagoras.r' 'scale.r'

LazyData:

true

VignetteBuilder:

knitr

Config/testthat/edition:

NeedsCompilation:

Packaged:

2025-06-19 22:30:24 UTC; vries171

Repository:

CRAN

Date/Publication:

2025-06-19 23:00:02 UTC

ggfields: Add Vector Field Layers to Ggplots

Description

Author(s)

Maintainer: Pepijn de Vries pepijn.devries@outlook.com (ORCID)

Arrows depicting a vector field

Description

Visualise vector fields (such as, electric/magnetic fields, wind speed, or water currents) with arrows as a layer in a ggplot.

Usage

GeomFields

geom_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,
  ...
)

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

Can be one of four things:

NULL: in that case data from the parent ggplot call is inherited.
data.frame: you need to assign the x and y aesthetics.
sf object: it should contain a geometry column with only POINT geometries.
stars object: it will be converted automatically to an sf object.

stat

The statistical transformation to use on the data for this layer. By default it is set to GeomFields() ("fields").

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. It can also be a named logical vector to finely select the aesthetics to display.

max_radius

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.

.angle_correction

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.

arrow

specification for arrow heads, as created by grid::arrow().

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().

...

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.

Format

An object of class GeomFields (inherits from GeomSegment, Geom, ggproto, gg) of length 8.

Details

Adds a layer with vector fields to a ggplot. In order to achieve this two special aesthetic are required: radius and angle.

Value

A layer which can be added to a ggplot.

Aesthetics

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.

Author(s)

Pepijn de Vries

Examples

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()
}

Stat method for geom_fields

Description

Prepares data before being handled by geom_fields()

Usage

StatFields

stat_fields(
  mapping = NULL,
  data = NULL,
  geom = "fields",
  position = "identity",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  ...
)

Arguments

mapping

data

Can be one of four things:

NULL: in that case data from the parent ggplot call is inherited.
data.frame: you need to assign the x and y aesthetics.
sf object: it should contain a geometry column with only POINT geometries.
stars object: it will be converted automatically to an sf object.

geom

The layer type for which the data is prepared. In this case "fields".

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

inherit.aes

...

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.

Format

An object of class StatFields (inherits from StatSf, Stat, ggproto, gg) of length 3.

Value

Returns a layer that can be further modified by geom_fields().

Author(s)

Pepijn de Vries

Examples

stat_fields()

Calculate correction for angle in the plot coordinate system

Description

The angle of a vector may be distorted when your plot uses a different coordinate system than the one for which the angle is specified. If data is a simple feature object (sf), the angle will be corrected for the displayed coordinate reference system (crs). When the crs is missing, an aspect ratio of 1 is assumed. For any other data, the angle is corrected for the aspect ratio in the plot.

Usage

angle_correction(data, panel_params, coord)

Arguments

data

fortified data used in a geom_fields(). Should at least contain numeric columns x, y and angle.

panel_params

panel parameters as returned by GeomFields$setup_params()

coord

A coord object.

Details

This function is used by default by geom_fields(). For more details on why this correction is required and how to customize corrections please see vignette("angle_correction").

Value

A data.frame with an additional angle_correction column. The corrected angle is given by angle_correction + angle.

Author(s)

Pepijn de Vries

Examples

if (requireNamespace("ggplot2") && requireNamespace("stars")) {
  library(ggplot2)
  library(stars)

  ggplot() +
    geom_fields(
      data    = seawatervelocity,
      mapping = aes(radius = as.numeric(v),
                    angle  = as.numeric(angle),
                    col    = as.numeric(v)),
 ## You can provide the `angle_correction()` as argument explicitly
 ## (it is already the default). Note that the plotted region requires
 ## hardly any correction for the angles.
                .angle_correction = angle_correction)
}

Annotate a ggplot with vector fields

Description

Functions exactly the same as geom_fields(), with that difference that this function does not train the x and y scales. This makes the data central, and uses this layer to support it. Consequently, annotation_fields() does not accept a stat argument.

Usage

annotation_fields(
  mapping = NULL,
  data = NULL,
  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,
  ...
)

Arguments

mapping

data

Can be one of four things:

NULL: in that case data from the parent ggplot call is inherited.
data.frame: you need to assign the x and y aesthetics.
sf object: it should contain a geometry column with only POINT geometries.
stars object: it will be converted automatically to an sf object.

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

max_radius

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.

.angle_correction

arrow

specification for arrow heads, as created by grid::arrow().

inherit.aes

...

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 ggplot2::layer_sf().

Author(s)

Pepijn de Vries

Examples

if (requireNamespace("stars") && requireNamespace("ggplot2")) {
  library(stars)
  library(ggplot2)

  data("seawatervelocity")
  sw_sub <- seawatervelocity[,8:13,1:5]
  
  ## Note that the `seawatervelocity` spans a much larger area,
  ## but the plot only focuses on `sw_sub`
  ggplot() +
    geom_stars(data = sw_sub) +
    annotation_fields(data = seawatervelocity,
                      aes(angle = as.numeric(atan2(vo, uo)),
                          radius = as.numeric(pythagoras(uo, vo)))) +
    labs(radius = "v [m/s]")
}

Key glyphs for 'radius' legends

Description

Each geom has an associated function that draws the key when the geom needs to be displayed in a legend. These functions are called ⁠draw_key_*()⁠, where * stands for the name of the respective key glyph. The key glyphs can be customized for individual geoms by providing a geom with the key_glyph argument (see layer() or examples below.)

Usage

draw_key_fields(data, params, size)

Arguments

data

A single row data frame containing the scaled aesthetics to display in this key

params

A list of additional parameters supplied to the geom.

size

Width and height of key in mm.

Details

The layer geom_fields() allows for a special aesthetic radius. This function draws a key glyph for this aesthetics, where the radius of the arrow corresponds with the scalar value listed with this radius. Note that the width of the key glyph cannot be adjusted by the aesthetic itself. Therefore, if your max_radius parameter exceeds the glyph width, you need to change the width of the guides yourself, see vignette("radius_aes") for more details.

Value

A grid grob

Author(s)

Pepijn de Vries

Examples

if (requireNamespace("ggplot2")) {
  library(ggplot2)
  p <- ggplot(economics, aes(date, psavert, color = "savings rate"))
  p + geom_line(key_glyph = "fields")
}

A helper function to calculate vector lengths

Description

Calculates the length of a vector using the Pythagorean theorem.

Usage

pythagoras(x, y)

Arguments

x

A numeric vector with the same length as y. It should represent the lengths of the first leg (cathetus) of right triangles.

y

A numeric vector with the same length as x. It should represent the lengths of the second leg (cathetus) of right triangles.

Value

Returns a numeric vector with the same length as x and y, reflecting the lengths of the hypotenuse of the right triangles.

Author(s)

Pepijn de Vries

Examples

pythagoras(x = c(1, 2), y = c(1, 2))

Vector field radius scales

Description

Scales to set up the visualisation of the radius aesthetic. These scales are also automatically used in plot guides. Note that scale_radius_identity() does not exist as it would be impossible to relate such a scale to the max_radius parameter. For more details see vignette("radius_aes").

Usage

scale_radius_continuous(..., range = c(1e-08, 1))

scale_radius_binned(..., range = c(1e-08, 1))

scale_radius_discrete(..., range = c(1e-08, 1))

Arguments

...

Arguments passed on to underpinning ⁠ggplot2::scale_*⁠ functions.

range

Relative output range of radii. Must lie between 0 and 1.

Value

An object of class Scale.

Author(s)

Pepijn de Vries

Examples

if (requireNamespace("ggplot2")) {
  library(ggplot2)
  data(seawatervelocity)
  
  g_num <-
    ggplot() +
    geom_fields(data = seawatervelocity,
                aes(radius = as.numeric(v), angle = as.numeric(angle)))
  g_discr <-
    ggplot() +
    geom_fields(data = seawatervelocity,
                aes(radius = cut(as.numeric(v), 4), angle = as.numeric(angle)))
                
  g_num + scale_radius_continuous()
  g_num + scale_radius_binned()
  g_discr + scale_radius_discrete()
}

A small subset of the global ocean physics analysis and forecast product

Description

A small subset of ocean currents data retrieved with CopernicusMarine from the source listed below serving as an example.

Format

A stars object with x, y, depth and time dimensions. It has the attributes vo (northward seawater velocity [m/s]) and uo (eastward seawater velocity [m/s]).

References

E.U. Copernicus Marine Service Information; Global Ocean Physics Analysis and Forecast - GLOBAL_ANALYSISFORECAST_PHY_001_024 (2016-10-14). doi:10.48670/moi-00016

Examples

data("seawatervelocity")

ggfields: Add Vector Field Layers to Ggplots

Description

Author(s)

See Also

Arrows depicting a vector field

Description

Usage

Arguments

Format

Details

Value

Aesthetics

Author(s)

Examples

Stat method for geom_fields

Description

Usage

Arguments

Format

Value

Author(s)

Examples

Calculate correction for angle in the plot coordinate system

Description

Usage

Arguments

Details

Value

Author(s)

Examples

Annotate a ggplot with vector fields

Description

Usage

Arguments

Value

Author(s)

Examples

Key glyphs for 'radius' legends

Description

Usage

Arguments

Details

Value

Author(s)

Examples

A helper function to calculate vector lengths

Description

Usage

Arguments

Value

Author(s)

Examples

Vector field radius scales

Description

Usage

Arguments

Value

Author(s)

Examples

A small subset of the global ocean physics analysis and forecast product

Description

Format

References

Examples