[R] Hydrology plots in R

[Deepayan Sarkar]

On Thu, Jul 22, 2010 at 7:56 AM, Sam Albers <tonightsthenight at gmail.com> wrote:
> Hello,
>
> I am trying to create a plot often seen in hydrodynamic work than includes a
> contour plot representing the water speed with arrows pointing in the
> direction of flow. Does anyone have any idea how I might add arrows based on
> wf$angle (in the example below) to the plot below?
>
> Thanks in advance!
>
> Sam
>
> library(lattice)
>
> speed <- runif(100, 0, 20)
> wf <- data.frame(speed)
> wf$width <- (1:10)
> wf$length <- rep(1:10, each=10)
> wf$angle <-runif(100, 0, 360)
>
> #How do I add arrows based on wf$angle within each coloured box to represent
> the direction of flow?
> #i don't have to use lattice. Just using it as an example.
> with(wf, contourplot(speed ~ width*length,
>                     region=TRUE,
>                     contour=FALSE
>                     ))


with(wf,
     levelplot(speed ~ width * length,
               angle = angle / 2 * pi,
               region = TRUE,
               contour = FALSE,
               panel = function(x, y, ..., subscripts, angle, scale = 0.45) {
                   panel.levelplot(x, y, ..., subscripts = subscripts)
                   panel.arrows(x[subscripts], y[subscripts],
                                x[subscripts] + scale * cos(angle[subscripts]),
                                y[subscripts] + scale * sin(angle[subscripts]),
                                length = 0.07)
               }))

-Deepayan