grd: Raster-like objects

In wk: Lightweight Well-Known Geometry Parsing

Raster-like objects

Description

grd() objects are just an array (any object with more than two dim()s) and a bounding box (a rct(), which may or may not have a wk_crs() attached). The ordering of the dimensions is y (indices increasing downwards), x (indices increasing to the right). This follows the ordering of as.raster()/rasterImage() and aligns with the printing of matrices.

Usage

grd(
  bbox = NULL,
  nx = NULL,
  ny = NULL,
  dx = NULL,
  dy = NULL,
  type = c("polygons", "corners", "centers")
)

grd_rct(data, bbox = rct(0, 0, dim(data)[2], dim(data)[1]))

grd_xy(data, bbox = rct(0, 0, dim(data)[2] - 1, dim(data)[1] - 1))

as_grd_rct(x, ...)

## S3 method for class 'wk_grd_rct'
as_grd_rct(x, ...)

## S3 method for class 'wk_grd_xy'
as_grd_rct(x, ...)

as_grd_xy(x, ...)

## S3 method for class 'wk_grd_xy'
as_grd_xy(x, ...)

## S3 method for class 'wk_grd_rct'
as_grd_xy(x, ...)

Arguments

bbox	A rct() containing the bounds and CRS of the object. You can specify a rct() with xmin > xmax or ymin > ymax which will flip the underlying data and return an object with a normalized bounding box and data.
nx, ny, dx, dy	Either a number of cells in the x- and y- directions or delta in the x- and y-directions (in which case bbox must be specified).
type	Use "polygons" to return a grid whose objects can be represented using an rct(); use "centers" to return a grid whose objects are the center of the rct() grid; use "corners" to return a grid along the corners of bbox.
data	An object with two or more dimensions. Most usefully, a matrix.
x	An object to convert to a grid
...	Passed to S3 methods

Value

• grd() returns a grd_rct() for ⁠type == "polygons⁠ or a grd_xy() otherwise.

• grd_rct() returns an object of class "wk_grd_rct".

• grd_xy() returns an object of class "wk_grd_xy".

Examples

# create a grid with no data (just for coordinates)
(grid <- grd(nx = 2, ny = 2))
as_rct(grid)
as_xy(grid)
plot(grid, border = "black")

# more usefully, wraps a matrix or nd array + bbox
# approx volcano in New Zealand Transverse Mercator
bbox <- rct(
  5917000,       1757000 + 870,
  5917000 + 610, 1757000,
  crs = "EPSG:2193"
)
(grid <- grd_rct(volcano, bbox))

# these come with a reasonable default plot method for matrix data
plot(grid)

# you can set the data or the bounding box after creation
grid$bbox <- rct(0, 0, 1, 1)

# subset by indices or rct
plot(grid[1:2, 1:2])
plot(grid[c(start = NA, stop = NA, step = 2), c(start = NA, stop = NA, step = 2)])
plot(grid[rct(0, 0, 0.5, 0.5)])

wk documentation built on Oct. 22, 2023, 9:07 a.m.