1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
|
# Arguments:
# u,v - the x (longitude) and y (latitude) offsets
# OR orientation and magnitude
# xpos,ypos - the centers of the vectors
# scale - the longest arrow as a proportion of the cell size
# headspan - the extent of the arrowhead as a proportion of cell size
# this function doesn't assume a 1:1 aspect ratio
vectorField<-function (u, v, xpos = NA, ypos = NA, scale = 1, headspan = 0.1,
vecspec = c("lonlat", "rad", "deg"), col = par("fg"))
{
udim <- dim(u)
if (is.na(xpos[1]))
xpos <- col(u)
if (is.na(ypos[1]))
ypos <- udim[1] - row(u) + 1
ymult <- getYmult()
if (match(vecspec[1], "lonlat", 0) == 0) {
if (match(vecspec[1], "deg", 0))
u <- pi * u/180
mag <- v
tempu <- v * cos(u)
v <- v * sin(u) * ymult
u <- tempu
}
else mag <- sqrt(u * u + v * v)
if (is.null(dim(xpos)))
maxmag <- 0.5 * max(diff(as.numeric(xpos)))/max(mag)
else maxmag <- 0.5 * max(diff(as.numeric(xpos[1, ])))/max(mag)
u2 <- u * scale * maxmag
v2 <- v * scale * maxmag
if (is.null(udim))
length = headspan
else length <- headspan * par("pin")[1]/udim[2]
arrows(xpos - u2, ypos - v2, xpos + u2, ypos + v2, length = length,
col = col)
}
|
