Plot a direction field on a existing map.

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.

See also

A map must first have been created with mapPlot().

Other functions related to maps: formatPosition(), lonlat2map(), lonlat2utm(), map2lonlat(), mapArrows(), mapAxis(), mapContour(), mapCoordinateSystem(), mapGrid(), mapImage(), mapLines(), mapLocator(), mapLongitudeLatitudeXY(), mapPlot(), mapPoints(), mapPolygon(), mapScalebar(), mapText(), mapTissot(), oceCRS(), shiftLongitude(), usrLonLat(), utm2lonlat()

Examples

# \donttest{ library(oce) data(coastlineWorld) par(mar=rep(2, 4)) mapPlot(coastlineWorld, longitudelim=c(-120,-55), latitudelim=c(35, 50), proj="+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')
#> Warning: zero-length arrow is of indeterminate angle and so skipped
#> Warning: zero-length arrow is of indeterminate angle and so skipped
#> Warning: zero-length arrow is of indeterminate angle and so skipped
# Color code by longitude, using thick lines col <- colormap(lonm)$zcol mapDirectionField(lonm, latm, 1, 0, scale=3, col=col, lwd=2)
# }