as.arrows: Add directional arrows from a SpatRaster to a plot

In terra: Spatial Data Analysis

Add directional arrows from a SpatRaster to a plot

Description

Create directional arrows and add these to a plot, typically used to represent vector fields such as wind directions, drainage flow directions, or other angular data.

Usage

as.arrows(x, unit=c("degrees", "radians", "flowdir"),
       arrow_length=NA,clockwise=FALSE, angle_from_h_axis=0,
       angle_from_x_axis=angle_from_h_axis, length=0,...)

Arguments

x	SpatRaster with values representing angles or directions
unit	Character. Unit of the angle values in x. One of "degrees", "radians" or "flowdir". See terrain for flowdir
arrow_length	Numeric. Length of the arrows to be plotted
clockwise	Logical. Default is FALSE. If TRUE, angles measured in radians or degrees are considered clockwise
angle_from_x_axis	Anti-clockwise angle from x (or horizontal) axis to the reference direction
angle_from_h_axis	Anti-clockwise angle from x (or horizontal) axis to the reference direction. In the case of northing wind direction it is often used angle_from_x_axis=90, unit="deg", clockwise=TRUE
length, ...	Additional graphical parameters passed to arrows

Author(s)

Emanuele Cordano

See Also

arrows, terrain

Examples

r <- rast(system.file("ex/elev_vinschgau.tif", package="terra"))
r <- aggregate(r, fact=2,fun=min)
d <- terrain(r, "flowdir")

plot(r,col=terrain.colors(10))
as.arrows(d, unit="flowdir", col="black")

terra documentation built on Aug. 22, 2026, 5:07 p.m.