Virtual grid modification

To modify a grid is to align an extent to the grid origin. Modification includes reducing or extending the area covered in either dimension. This implies a new extent, snapped to the grain of the origin grid, and a new dimension (ncol, nrow).

vcrop(x, dimension, extent = NULL, ..., snap = "out")

Arguments

x

extent of candidate grid (vector of xmin, xmax, ymin, ymax)

dimension

integer ncol, nrow

extent

numeric extent xmin,xmax,ymin,ymax

...

ignored

snap

one of "out" (default), "near", or "in"

Value

A list with two components:

extent

numeric vector (xmin, xmax, ymin, ymax) - the new extent, snapped to grid alignment

dimension

integer vector (ncol, nrow) - the dimension of the modified grid

Details

This works for any grid: the input extent can be within the original, an extension of the original, or completely non-intersecting the original grid.

See also

align_extent() for just the extent snapping, extent_dimension() for just the dimension calculation

Examples

## any arbitrary extent
x <- c(sort(runif(2, -180, 180)), sort(runif(2, -90, 90)))
print(x)
#> [1] -59.14113  25.21618 -55.52675  17.32730
vcrop(x, c(360, 180), c(-180, 180, -90, 90))
#> $extent
#> [1] -60  26 -56  18
#> 
#> $dimension
#> [1] 86 74
#> 

## crop to a smaller region
vcrop(c(0, 10, 0, 10), c(360, 180), c(-180, 180, -90, 90))
#> $extent
#> [1]  0 10  0 10
#> 
#> $dimension
#> [1] 10 10
#> 

## extend beyond original (snapped to grid)
vcrop(c(-200, 200, -100, 100), c(360, 180), c(-180, 180, -90, 90))
#> $extent
#> [1] -200  200 -100  100
#> 
#> $dimension
#> [1] 400 200
#>