Each point falls in a square cell of size_km on a Lambert azimuthal
equal-area projection centred on the points (on the sphere of WGS84's
authalic radius), so every block covers the same ground wherever it lies –
which a grid in degrees does not: a degree of longitude is 111 km at the
equator and 71 km at 50 degrees.
Usage
equal_area_blocks(x, y, size_km, coords = c("lonlat", "metres"), centre = NULL)Arguments
- x, y
Longitude and latitude in degrees (
coords = "lonlat"), or easting and northing in metres of an equal-area projection of yours (coords = "metres").- size_km
The side of a block, in km.
- coords
"lonlat" (the default) or "metres".
- centre
For "lonlat": the projection's centre,
c(longitude, latitude). NULL: the points' own means.
Value
A character vector, one block per point (the cell's column and row, "i_j"), with the size and the projection as attributes.
Examples
ex <- example_landscape()
blk <- equal_area_blocks(ex$profiles$x, ex$profiles$y, size_km = 2)
length(unique(blk)) # blocks holding a profile
#> [1] 60
table(table(blk)) # how many blocks hold 1, 2, ... profiles
#>
#> 1 2 3 4 6 8 10 16 21
#> 34 12 5 1 3 1 2 1 1