vectorplot: Vector plots of Raster objects.
In rasterVis: Visualization methods for the raster package

Description Usage Arguments Author(s) References See Also Examples

vectorplot displays vector fields from Raster objects using arrows.

streamplot displays streamlines with a procedure inspired by the FROLIC algorithm (see references): for each point (droplet) of a jittered regular grid, a short streamline portion (streamlet) is calculated by integrating the underlying vector field at that point. The main color of each streamlet indicates local vector magnitude (slope). Streamlets are composed of points whose sizes, positions and color degradation encode the local vector direction (aspect).

## S4 method for signature 'Raster'
vectorplot(object, layers,
            narrows=2e3, lwd.arrows=0.6, length=unit(5e-2, 'npc'),
            maxpixels=1e5, region=TRUE,  
            isField=FALSE, reverse=FALSE, unit='radians', ...)

## S4 method for signature 'Raster'
streamplot(object, layers,
            droplet = list(), streamlet = list(),
            par.settings=streamTheme(),
            isField = FALSE, reverse=FALSE, 
            parallel=TRUE, mc.cores=detectCores(), cl=NULL,
            ...)

## S4 method for signature 'RasterStack'
streamplot(object, layers,
            droplet = list(), streamlet = list(),
            par.settings=streamTheme(),
            isField = FALSE, reverse=FALSE, 
            parallel=TRUE, mc.cores=detectCores(), cl=NULL,
            ...)

`object`	A Raster object. If `isField=FALSE` the vector field is calculated internally from the result of `terrain`.
`layers`	A numeric or character which should indicate the layers to be displayed.
`maxpixels`	A numeric, number of cells to be shown if `region=TRUE`.
`narrows`	A numeric, number of arrows.
`lwd.arrows`	Numeric, width of the lines of the arrows
`length`	Unit, extent of the arrow head.
`droplet`	A list whose elements define the droplet configuration: cropExtent: Percentage of the object extent to be cropped (default .97) to avoid droplets at boundaries pc: Percentage of cells to be used for the streamlets calculation (default .5)
`streamlet`	A list whose elements define the streamlet configuration: L: length of the streamlet (number of points, default 10) h: streamlet calculation step (default `mean(res(object))`).
`par.settings`	A list to define the graphical parameters. For `streamplot` there is an specific theme, `streamTheme`.
`parallel`	Logical, TRUE (default) to use `parallel` package.
`cl`	a cluster object. Read the help page of `parLapply` for details.
`mc.cores`	The number of cores to use if `parallel=TRUE` and no `cl` is provided. Read the help page of `mclapply` for details.
`region`	Logical, if `TRUE` the region is displayed with `vectorplot` using `panel.levelplot.raster`
`reverse`	Logical, TRUE if arrows or streamlets go against the direction of the gradient.
`isField`	Logical, if `TRUE` (the object is a vector field), `object` must be a Raster* with two layers, slope and aspect (in this order), following the philosophy of `terrain`.
`unit`	Character, angle units of the `aspect` layer if `isField=TRUE`: 'radians' or 'degrees'.
`...`	Additional arguments for `levelplot`

Oscar Perpiñán Lamigueiro

R. Wegenkittl and E. Gröller, Fast Oriented Line Integral Convolution for Vector Field Visualization via the Internet, Proceedings IEEE Visualization ’97, 1997, http://www.cg.tuwien.ac.at/research/vis-dyn-syst/frolic/frolic_crc.pdf

panel.arrows, levelplot, terrain, mclapply, parLapply

## Not run: 
proj <- CRS('+proj=longlat +datum=WGS84')

df <- expand.grid(x=seq(-2, 2, .01), y=seq(-2, 2, .01))
df$z <- with(df, (3*x^2 + y)*exp(-x^2-y^2))
r1 <- rasterFromXYZ(df, crs=proj)
df$z <- with(df, x*exp(-x^2-y^2))
r2 <- rasterFromXYZ(df, crs=proj)
df$z <- with(df, y*exp(-x^2-y^2))
r3 <- rasterFromXYZ(df, crs=proj)
s <- stack(r1, r2, r3)
names(s) <- c('R1', 'R2', 'R3')

vectorplot(r1)
vectorplot(r2, par.settings=RdBuTheme())
vectorplot(r3, par.settings=PuOrTheme())


## If no cluster is provided, streamplot uses parallel::mclapply except
## with Windows. Therefore, next code could spend a long time under
## Windows.
streamplot(r1)

## With a cluster
hosts <- rep('localhost', 4)
cl <- makeCluster(hosts)
streamplot(r2, cl=cl,
           par.settings=streamTheme(symbol=brewer.pal(n=5,
                                                      name='Reds')))
stopCluster(cl)

## Without parallel
streamplot(r3, parallel=FALSE,
           par.settings=streamTheme(symbol=brewer.pal(n=5,
                                                      name='Greens')))

## Configuration of droplets and streamlets
streamplot(s, layout=c(1, 3), droplet=list(pc=.2), streamlet=list(L=20),
           par.settings=streamTheme(cex=.6))

## End(Not run)