is.in.grid-methods: Checks if the points (xy$x, xy$y) are in the 'fvcom.grid'...
In ocean: Biophysical Oceanography Tools

Checks if the points (xy$x, xy$y) are in the fvcom.grid grid.

`grid`	A `fvcom.grid` instance.
`xy`	A `data.frame` with components `x` and `y` with the x and y locations of the points.
`units`	Either 'll' for latitude and longitude or 'm' for meters.

A vector of logical values of length nrow(xy). The ith element is TRUE if (xy$x[i], xy$y[i]) is in grid and FALSE otherwise.

{
# Create a regular grid of test points
nodes = get.nodes(ocean.demo.grid)
lattice.grid = expand.grid(x=seq(min(nodes$x), max(nodes$x), len=25),
                           y=seq(min(nodes$y), max(nodes$y), len=25))
# Check which points are in the grid
in.grid = is.in.grid(ocean.demo.grid, lattice.grid, units="m")
# Plot the points that are in the grid
with(lattice.grid[in.grid,], plot(x, y))
}