Display magnitude/direction vectors

Display magnitude/direction vectors as arrows on an existing plot.

Usage

vectorField(u,v,xpos=NA,ypos=NA,scale=1,headspan=0.1,
 vecspec=c("lonlat","rad","deg"),col=par("fg"))

Arguments

u,v

x (longitude) and y (latitude) offsets OR orientation and magnitude in either radians or degrees. See details.

xpos,ypos

The centers of the vectors in user units.

scale

The proportion of each cell that the maximal vector will fill. See details.

headspan

The extent of the heads of the arrows as a proportion of cell size.

vecspec

How the vectors are described. See details

col

Color(s) for the arrows.

Value

nil

Details

vectorField displays arrows on an existing plot. Each arrow is specified by a position on the plot xpos,ypos and either x/y offsets or orientation and magnitude. The default is x/y offsets, and the user must specify whether radians or degrees are used if the orientation/magnitude option is used.

If the first four arguments are matrices, there must be no missing values. If these arguments are vectors, the calculation of the scaling of the magnitudes and length of the arrowheads may be slightly different.

Author

Jim Lemon (original code by Robin Hankin and Brian Ripley)

See also

arrows

Examples

 if (FALSE) {
  # this requires the maps package, and just wouldn't pass check
  require(maps)
  map("world",xlim=c(110,155),ylim=c(-40,-10))
  par(xpd=TRUE)
  text(132,-5,"Approximate magnetic deviation - Australia",cex=1.5)
  par(xpd=FALSE)
  long<-rep(seq(117.5,152.5,by=5),6)
  lat<-rep(c(-12.5,-17.5,-22.5,-27.5,-32.5,-37.5),each=8)
  # just show the direction, don't have a magnitude difference
  mag<-rep(1,48)
  devdeg<-c(110,98,85,65,65,65,65,65,
   115,100,90,80,72,66,63,55,
   130,100,90,82,72,67,62,54,
   122,111,95,86,70,67,56,48,
   118,116,110,87,74,68,62,45,
   128,115,107,90,78,66,53,45)
  vectorField(devdeg,mag,long,lat,scale=0.7,vecspec="deg")
 }
 # do a magnitude/direction plot with radians
 plot(1:10,type="n",main="Random vectors")
 mag<-runif(100)+1
 dir<-runif(100)*2*pi
 xpos<-rep(1:10,10)
 ypos<-rep(1:10,each=10)
 vectorcol<-sample(colors(),100)
 vectorField(dir,mag,xpos,ypos,scale=0.8,vecspec="rad",col=vectorcol)