Introducing ggrgl - a 3d extension to ggplot

2020-12-02

ggrgl

Lifecycle: experimental

ggrgl extends ggplot2 into the third dimension.

ggrgl does this by adding a new z aesthetic which is respected when a plot is rendered to the {devoutrgl} device which renders to OpenGL via {rgl}.

Because {devoutrgl} is an interactive device, the view of the plot may be manipulated by the user - zoom, rotate, change field-of-view etc.

Slideshow

Note: interactive 3d plots cannot be displayed in a github README file, and static images or animated gifs are used here instead.

Visit the pkgdown online documentation to view plots which can be manipulated in the browser.

Installation

A lot of support packages are needed for ggrgl - most of which should already be installed if you have ggplot.

Custom packages which are needed (and not currently on CRAN):

  • devout - The core package for writing graphics devices using R (rather than C).
  • devoutrgl - a graphics device which renders to {rgl}
  • triangular - decompaose polygons into triangles for 3d rendering. Much faster than rgl::triangulate()
  • snowcrash - a package for encoding objects as images - needed to circumvent limitations in the device system provided by R
  • cryogenic - a package for capturing a call to be evaluated later. Calls to generate 3d geometry are generated when plot object is created, but not executed until later when the plot is actually rendered to screen.

You can install from GitHub with:

# install.package('remotes')
remotes::install_github('coolbutuseless/devout')
remotes::install_github('coolbutuseless/devoutrgl')
remotes::install_github('coolbutuseless/triangular')
remotes::install_github('coolbutuseless/snowcrash')
remotes::install_github('coolbutuseless/cryogenic')
remotes::install_github('coolbutuseless/ggrgl', ref='main')

New z Aesthetic

The new z aesthetic works the same as the x and y aesthetics in ggplot2.

z may be mapped to a data variable or set to a constant.

New Extrusion Aesthetics

When graphical elements have a z value they are raised above the ground.

By setting extrude = TRUE (on geoms which support it), then the raised element is connected to the ground as if it were extruded from it.

New aesthetics control the appearance of the extruded faces and edges:

aesthetic Description default
extrude_z Lower limit of extrusion 0.05
extrude_face_fill Extruded face colour grey20
extrude_face_alpha Extruded face alpha 1
extrude_edge_colour Edge colour for extrusion NA
extrude_edge_alpha Edge alpha for extrusion 1
extrude_edge_size Width of line for extruded edges 1

3-dimensional Geometry Types: z and 3d

ggrgl defines 2 classes of geoms: z and 3d

  • z geoms are identical to their ggplot2 counterparts, except the entire shape may be raised (as a unit) in the z direction. The resulting geometry will still be planar, and parallel to the original plotting surface.
  • 3d geoms allow for full specification of (x, y, z) locations. Their orientation is not constrained to be planar, or parallel to the original plotting surface.

Click on a geom in the following table to view its vignette

ggplot2 Planar Z offset 3d
geom_bar geom_bar_z
geom_contour geom_contour_z
geom_contour_filled geom_contour_filled_z
geom_density geom_density_z
geom_line geom_line_3d
geom_path geom_path_3d
geom_point geom_point_z geom_sphere_3d
geom_polygon geom_polygon_z
geom_rect geom_rect_z
geom_ribbon geom_ribbon_z
geom_segment geom_segment_3d
geom_text geom_text_z
geom_tile geom_tile_z

Vignettes

There are vignettes on all the new geoms in this package, see links in the table above or click on an image below

Some vignettes with some details of the implementation and usage are:

  • Technical Overview gives some details on how the 3d geometry is communicated internally
  • Z Scaling shows examples how the scaling of the Z coordinate may be controlled.
  • Keep 2d ‘shadows’ demonstrates how the 2d shadow of 3d geometry may be kept for some supported geoms.

To see all vignettes see the online documentation

Example - A Basic 3d Bar Plot with geom_bar_z()

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Use `geom_bar_z` and set `z` to 200 and use extrusion
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
p <- ggplot(mpg) +
  geom_bar_z(aes(x=class, fill=class), colour='black', z=200, extrude=TRUE)


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Render Plot in 3d with {devoutrgl}
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
devoutrgl::rgldev()
p
invisible(dev.off())

Acknowledgements

  • Hadley Wickham, Thomas Lin Pedersen and others for developing and maintaining ggplot2
  • Michael Sumner + Tyler Morgan-Wall on twitter for their in-depth technical advice on graphics and 3d in R
  • R Core for developing and maintaining the language.
  • CRAN maintainers, for patiently shepherding packages onto CRAN and maintaining the repository