Create a full grid from a set of coordinates

resample_grid() creates a rectangular grid around supplied coordinates by resampling evenly spaced points between the minimum and maximum values of each coordinate dimension. The grid can optionally be reduced to a convex or concave hull around the supplied coordinates.

Usage

resample_grid(coords2D, resample = 100, padding = 1.2, hull = NULL, alpha = 1, 
  plot = FALSE)

Arguments

coords2D

a 2-column matrix data frame of coordinates with the x-coordinates in the first column and the y-coordinates in the second column. The ranges of each column will be used to create the resampled grid.

resample

the number of points (or pixels) in the x and y dimensions over which to create the grid. Default is 100 for a kriged surface of 100x100=10,000 pixels.

padding

a number representing how much to expand the grid beyond the ranges of the x- and y-coordinates. For example, padding = 1.2 (the default) expands the grid by 20% of the coordinates' ranges in each direction. Must be a number greater than or equal to 1. Large numbers imply greater extrapolation, and whatever padding is added will be negated if hull is specified.

hull

method to restrict the grid to an alpha hull using alphahull] or concaveman packages. Default is `NULL` and no hull will be calculated.

alpha

when hull != NULL, the alpha value used to create the hull. Passed to ahull or concaveman.

plot

Logical. When hull is specified, whether to plot the resulting hull overlayed over the original grid. Default is TRUE.

Value

A data frame with two columns, x and y, containing the resampled coordinate grid. When hull is specified, any points not in the hull will be absent.

See also

krige_surf, which uses resample_grid for kriging.

ahull and inahull, or concaveman for creating the hull.

Examples

data("warps")

warps_fnc <- as_fnc_df(warps)

# hull with plot to see the hull
grid <- resample_grid(warps_fnc[c("x", "y")],
                      hull = "concaveman", plot = TRUE)

str(grid)
#> 'data.frame':	4900 obs. of  2 variables:
#>  $ x: num  -0.186 -0.182 -0.178 -0.174 -0.17 ...
#>  $ y: num  -0.0499 -0.0499 -0.0499 -0.0499 -0.0499 ...
#>  - attr(*, "hull")= chr "concaveman"
#>  - attr(*, "alpha")= num 1

if (FALSE) {
# Alpha hull with plot to see the hull
grid <- resample_grid(warps_fnc[c("x", "y")],
                      hull = "alphahull", plot = TRUE)
}