README.md
In hypertidy/vaster: Tools for Raster Grid Logic

vaster

The goal of vaster is to provide grid logic without complication added by data and format details.

You can install the development version of vaster from GitHub with:

# install.packages("devtools")
devtools::install_github("hypertidy/vaster")

See?

library(vaster)
set.seed(1)
x <- c(sort(runif(2, -20, 160)), sort(runif(2, -80, 10)))
names(x) <- c("xmin", "xmax", "ymin", "ymax")
print(x)
#>       xmin       xmax       ymin       ymax 
#>  27.791559  46.982302 -28.443197   1.738701
## all we need is a extent and dimension, we want to align to that grid
v <- vcrop(x,  c(360, 180) /3, extent = c(-180, 180, -90, 90))
plot(NA, xlim = v$extent[1:2], ylim = v$extent[3:4], asp = "")
g_along <- function(x, n) seq(x[1], x[2], length.out = n)
abline(v = v$extent[1:2], h = v$extent[3:4], lwd = 2)
abline(v = g_along(v$extent[1:2], v$dimension[1]), h = g_along(v$extent[3:4], v$dimension[2]), col = "grey")

## these points were used to crop the existing grid, they don't define its alignment
points(x[1:2], x[3:4], pch = "+")

All of the helper functions from the raster package are included, and every function is one of dimension, extent (when needed) in that order.

A grid of the world in 9x5 degree squares, we only need the dimension and extent to get the corners in x, y.

ex <- c(-180, 180, -90, 90)
dm <- c(40, 36)

plot_extent(ex)
abline(v = x_corner(dm, ex), h = y_corner(dm, ex))

Now add the centre points.

plot_extent(ex)
points(x_centre(dm, ex), rep(y_centre(dm, ex)[1], length.out = dm[1]))

We only get the margins from x_corner/x_centre so we go to a cell based function.

## how many cells?
cells <- seq_len(prod(dm))
plot_extent(ex)
points(xy_from_cell(dm, ex, cells))

Other functions return cells.

xy <- cbind(runif(50, -180, 180), runif(50, -90, 90))
cells <- cell_from_xy(dm, ex, xy)
plot_extent(ex)
points(xy_from_cell(dm, ex, cells), col = "red")
points(xy, pch = "+")