Compute the flow path (drainage path) starting at a given point. See package `gdistance`

for more path computations.

## Arguments

- x
RasterLayer of flow direction (as can be created with `terrain`

- p
starting point. Either two numbers: x (longitude) and y (latitude) coordinates; or a single cell number

- ...
additional arguments (none implemented)

## Value

numeric (cell numbers)

## Examples

```
data(volcano)
v <- raster(volcano, xmn=2667400, xmx=2668010, ymn=6478700, ymx=6479570, crs="+init=epsg:27200")
fd <- terrain(v, opt = "flowdir")
path <- flowPath(fd, 2407)
xy <- xyFromCell(fd, path)
plot(v)
lines(xy)
```