I have a big raster which has value of 1 in each cell
r <- terra::rast(ncols=129600,
nrows=64800,
xmin=-180,
xmax=180,
ymin=-90,
ymax=90,
resolution = 0.002777778,
crs="+proj=longlat +datum=WGS84",
vals = 1)
I have a csv file that contains lon, lat and value
dat <- structure(list(lat = c(81.3152777777778, 81.3125, 81.3097222222222, 81.3069444444444, 81.2597222222222,
81.2569444444445, 81.2541666666667, 81.2513888888889, 81.2486111111111, 81.2458333333333),
lon = c(-19.9986111111111, -19.9986111111111, -19.9986111111111, -19.9986111111111, -19.9986111111111,
-19.9986111111111, -19.9986111111111, -19.9986111111111, -19.9986111111111, -19.9986111111111),
value = c(0.432098765432099, 0.432098765432099, 0.432098765432099, 0.432098765432099, 0.493827160493827,
0.506172839506173, 0.45679012345679, 0.407407407407407, 0.358024691358025, 0.308641975308642)),
row.names = c(NA, -10L), class = c("data.table", "data.frame"))
One thing to note is that dat is just a snapshot of the actual data I have and is actually is an irregular grid.
What I want to do is to fill the raster r with the value in dat using the lat/lon in dat.
To elaborate on this, for every lat/lon in dat, use its corresponding value to fill in the value in r. So when I tried to convert dat into a raster so that I can do
For those lat/lon that are not present in dat but are present in r, leave the default value to 1.
You can make use of terra::rasterize() with background = 1 to get your desired raster, as far as I understand:
# data.table to data.frame
dat <- as.data.frame(dat)
# create vector
v <- terra::vect(dat, geom = c("lat", "lon"), crs = "+proj=longlat +datum=WGS84")
# burn values from points to raster
terra::rasterize(x = v, y = r, field = "value", background = 1)
#> class : SpatRaster
#> dimensions : 180, 360, 1 (nrow, ncol, nlyr)
#> resolution : 0.002777778, 0.002777778 (x, y)
#> extent : -180, 180, -90, 90 (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=longlat +datum=WGS84 +no_defs
#> source : memory
#> name : lyr.1
#> min value : 0.308642
#> max value : 1
You would not need to specify vals = 1 in r <- rast() here since the grid is only used for geometry purposes.