R: Add a Direction Field to an Existing Map

mapDirectionField {oce}

R Documentation

Add a Direction Field to an Existing Map

Description

Plot a direction field on a existing map.

Usage

mapDirectionField(
  longitude,
  latitude,
  u,
  v,
  scale = 1,
  length = 0.05,
  code = 2,
  col = par("fg"),
  ...
)

Arguments

`longitude`, `latitude`	numeric vectors of the starting points for arrows.
`u`, `v`	numeric vectors of the components of a vector to be shown as a direction field.
`scale`	latitude degrees per unit of `u` or `v`.
`length`	length of arrow heads, passed to `arrows()`.
`code`	code of arrows, passed to `arrows()`.
`col`	color of arrows. This may be a single color, or a matrix of colors of the same dimension as `u`.
`...`	optional arguments passed to `arrows()`, e.g. `angle` and `lwd` can be useful in differentiating different fields.

Details

Adds arrows for a direction field on an existing map. There are different possibilities for how longitude, latitude and u and v match up. In one common case, all four of these are matrices, e.g. output from a numerical model. In another, longitude and latitude are the coordinates along the matrices, and are thus stored in vectors with lengths that match appropriately.

Sample of Usage

library(oce)
data(coastlineWorld)
par(mar=rep(2, 4))
mapPlot(coastlineWorld, longitudelim=c(-120,-55), latitudelim=c(35, 50),
        projection="+proj=laea +lat0=40 +lat1=60 +lon_0=-110")
lon <- seq(-120, -60, 15)
lat <- 45 + seq(-15, 15, 5)
lonm <- matrix(expand.grid(lon, lat)[, 1], nrow=length(lon))
latm <- matrix(expand.grid(lon, lat)[, 2], nrow=length(lon))
# vectors pointed 45 degrees clockwise from north
u <- matrix(1/sqrt(2), nrow=length(lon), ncol=length(lat))
v <- matrix(1/sqrt(2), nrow=length(lon), ncol=length(lat))
mapDirectionField(lon, lat, u, v, scale=3)
mapDirectionField(lonm, latm, 0, 1, scale=3, col="red")
# Color code by longitude, using thick lines
col <- colormap(lonm)$zcol
mapDirectionField(lonm, latm, 1, 0, scale=3, col=col, lwd=2)

Author(s)

Dan Kelley