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Write raster data to a NetCDF file

writeCDF.Rd

Write a SpatRaster or SpatRasterDataset to a NetCDF file.

When using a SpatRasterDataset, the varname, longname, and unit should be set in the object (see examples).

Always use the ".nc" or ".cdf" file extension to assure that the file can be properly read again by GDAL

You can write multiple rasters (variables) that are two (x, y), three (x, y, z or x, y, time) or four dimensional (x, y, z, time).

See depth and time for specifying the axes of the thrid and/or fourth dimension(s).

Usage

# S4 method for class 'SpatRaster'
writeCDF(x, filename, varname, longname="", unit="", split=FALSE, ...)

# S4 method for class 'SpatRasterDataset'
writeCDF(x, filename, overwrite=FALSE, timename="time", atts="", 
    gridmap="", prec="float", compression=NA, missval, ...)

Arguments

x

SpatRaster or SpatRasterDataset

filename

character. Output filename

varname

character. Name of the dataset

longname

character. Long name of the dataset

unit

character. Unit of the data

split

logical. If TRUE each layer of x is treated as a sub-dataset

atts

character. A vector of additional global attributes to write. The must be formatted like c("x=a value", "y=abc")

gridmap

character. The crs is always written to the file in standard formats. With this argument you can also write the format commonly used in netcdf files. Something like c("grid_mapping_name=lambert_azimuthal_equal_area", "longitude_of_projection_origin=10", "latitude_of_projection_origin=52", "false_easting=4321000", "false_northing=3210000")

overwrite

logical. If TRUE, filename is overwritten

timename

character. The name of the "time" dimension

prec

character. One of "double", "float", "integer", "short", "byte" or "char"

compression

Can be set to an integer between 1 (least compression) and 9 (most compression)

missval

numeric, the number used to indicate missing values

...

additional arguments passed on to the SpatRasterDataset method, and from there possibly to ncvar_def

Value

SpatRaster or SpatDataSet

See also

see writeRaster for writing other file formats

Examples


f <- system.file("ex/elev.tif", package="terra")
r <- rast(f)
fname <- paste0(tempfile(), ".nc")
rr <- writeCDF(r, fname, overwrite=TRUE, varname="alt", 
      longname="elevation in m above sea level", unit="m")

a <- rast(ncols=5, nrows=5, nl=50)
values(a) <- 1:prod(dim(a))
time(a) <- as.Date("2020-12-31") + 1:nlyr(a)
aa <- writeCDF(a, fname, overwrite=TRUE, varname="power", 
      longname="my nice data", unit="U/Pa")

b <- sqrt(a)
s <- sds(a, b)
names(s) <- c("temp", "prec")
longnames(s) <- c("temperature (C)", "precipitation (mm)")
units(s) <- c("°C", "mm")
ss <- writeCDF(s, fname, overwrite=TRUE)

# four dimensional 
r1 <- rast(nrow=5, ncol=5, vals=1:100, nlyr=4)
depth(r1) <- c(0, 2, 0, 2)
time(r1) <- c(as.Date("2012-12-12") + c(1,1,2,2))
depthName(r1) <- "angle"

r2 <- rast(nrow=5, ncol=5, vals=1:150, nlyr=6)
depth(r2) <- c(10, 10, 20, 20, 30, 30)
time(r2) <- c(as.Date("2012-12-12") + c(1:2, 1:2, 1:2))
depthName(r2) <- "height"
depthUnit(r2) <- "cm"

s <- sds(r1, r2)
names(s) <- c("TH", "DBZH")
units(s) <- c("-", "Pa")
x <- writeCDF(s, filename = fname, overwrite=TRUE)
#> Warning: GDAL Message 1: dimension #1 (angle) is not a Time dimension.
#> Warning: GDAL Message 1: dimension #1 (time) is not a Time dimension.
#> Warning: GDAL Message 1: dimension #0 (height) is not a Time dimension.
x[1]
#> class       : SpatRaster 
#> dimensions  : 5, 5, 4  (nrow, ncol, nlyr)
#> resolution  : 72, 36  (x, y)
#> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
#> coord. ref. : lon/lat WGS 84 (CRS84) (OGC:CRS84) 
#> source      : file23c41b440d13.nc:TH 
#> varname     : TH 
#> names       : TH_angle=0_1, TH_angle=2_1, TH_angle=0_2, TH_angle=2_2 
#> unit        :            -,            -,            -,            - 
#> depth       : 0 to 2 (angle: 2 steps) 
#> time (days) : 2012-12-13 to 2012-12-14 (2 steps) 
time(x[1])
#> [1] "2012-12-13" "2012-12-13" "2012-12-14" "2012-12-14"
depth(x[1])
#> [1] 0 2 0 2

x[2]
#> class       : SpatRaster 
#> dimensions  : 5, 5, 6  (nrow, ncol, nlyr)
#> resolution  : 72, 36  (x, y)
#> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
#> coord. ref. : lon/lat WGS 84 (CRS84) (OGC:CRS84) 
#> source      : file23c41b440d13.nc:DBZH 
#> varname     : DBZH 
#> names       : DBZH_~=10_1, DBZH_~=10_2, DBZH_~=20_1, DBZH_~=20_2, DBZH_~=30_1, DBZH_~=30_2 
#> unit        :          Pa,          Pa,          Pa,          Pa,          Pa,          Pa 
#> depth       : 10 to 30 (height [cm]: 3 steps) 
#> time (days) : 2012-12-13 to 2012-12-14 (2 steps) 
time(x[2])
#> [1] "2012-12-13" "2012-12-14" "2012-12-13" "2012-12-14" "2012-12-13"
#> [6] "2012-12-14"
depth(x[2])
#> [1] 10 10 20 20 30 30

# for CRAN
file.remove(fname)
#> [1] TRUE