Calculate correction for angle in the plot coordinate system

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.

Value

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

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").

Author

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)
}
#> Loading required package: abind
#> Loading required package: sf
#> Linking to GEOS 3.12.1, GDAL 3.8.4, PROJ 9.4.0; sf_use_s2() is TRUE
#> Angle correction between 0.00 and 0.00 radials