7.8 Convert from and to Raster\(^*\) or SpatRaster objects

7.8 Convert from and to `Raster`\(^*\) or `SpatRaster` objects

When you need to convert a stars object to a Raster\(^*\) or SpatRaster object, you can use the as() function as follows:

(
# to Raster* object
prcp_tmax_PRISM_m8_y09_rb <- as(prcp_tmax_PRISM_m8_y09, "Raster")
)

class      : RasterBrick 
dimensions : 20, 20, 400, 10  (nrow, ncol, ncell, nlayers)
resolution : 0.04166667, 0.04166667  (x, y)
extent     : -121.7292, -120.8958, 45.8125, 46.64583  (xmin, xmax, ymin, ymax)
crs        : +proj=longlat +datum=NAD83 +no_defs 
source     : memory
names      : layer.1, layer.2, layer.3, layer.4, layer.5, layer.6, layer.7, layer.8, layer.9, layer.10 
min values :       0,       0,       0,       0,       0,       0,       0,       0,       0,        0 
max values :   0.019,  18.888,  30.851,   4.287,   0.797,   0.003,   3.698,   1.801,   0.000,    0.000 
time       : 2009-08-11, 2009-08-12, 2009-08-13, 2009-08-14, 2009-08-15, 2009-08-16, 2009-08-17, 2009-08-18, 2009-08-19, 2009-08-20

(
# to SpatRaster
prcp_tmax_PRISM_m8_y09_sr <- as(prcp_tmax_PRISM_m8_y09, "SpatRaster")
)

class       : SpatRaster 
dimensions  : 20, 20, 10  (nrow, ncol, nlyr)
resolution  : 0.04166667, 0.04166667  (x, y)
extent      : -121.7292, -120.8958, 45.8125, 46.64583  (xmin, xmax, ymin, ymax)
coord. ref. : lon/lat NAD83 (EPSG:4269) 
source      : memory 
names       : date2~08-11, date2~08-12, date2~08-13, date2~08-14, date2~08-15, date2~08-16, ... 
min values  :           0,           0,           0,           0,           0,           0, ... 
max values  :       0.019,      18.888,      30.851,       4.287,       0.797,       0.003, ...

As you can see, date values in prcp_tmax_PRISM_m8_y09 appear in the time dimension of prcp_tmax_PRISM_m8_y09_rb (RasterBrick). However, in prcp_tmax_PRISM_m8_y09_sr (SpatRaster), date values appear in the names dimension with date added as prefix to the original date values.

Note also that the conversion was done for only the ppt attribute. This is simply because the raster and terrapackage does not accommodate multiple attributes of 3-dimensional array. So, if you want a RasterBrick or SpatRaster of the tmax data, then you need to do the following:

(
# to RasterBrick
tmax_PRISM_m8_y09_rb <- as(prcp_tmax_PRISM_m8_y09["tmax",,,], "Raster")
)

class      : RasterBrick 
dimensions : 20, 20, 400, 10  (nrow, ncol, ncell, nlayers)
resolution : 0.04166667, 0.04166667  (x, y)
extent     : -121.7292, -120.8958, 45.8125, 46.64583  (xmin, xmax, ymin, ymax)
crs        : +proj=longlat +datum=NAD83 +no_defs 
source     : memory
names      : layer.1, layer.2, layer.3, layer.4, layer.5, layer.6, layer.7, layer.8, layer.9, layer.10 
min values :  10.188,   8.811,   6.811,   3.640,   1.833,   6.780,  10.318,  14.270,  18.281,   19.818 
max values :  29.842,  28.892,  27.123,  23.171,  21.858,  24.690,  27.740,  32.906,  35.568,   39.707 
time       : 2009-08-11, 2009-08-12, 2009-08-13, 2009-08-14, 2009-08-15, 2009-08-16, 2009-08-17, 2009-08-18, 2009-08-19, 2009-08-20

(
# to SpatRaster
tmax_PRISM_m8_y09_sr <- as(prcp_tmax_PRISM_m8_y09["tmax",,,], "SpatRaster")
)

class       : SpatRaster 
dimensions  : 20, 20, 10  (nrow, ncol, nlyr)
resolution  : 0.04166667, 0.04166667  (x, y)
extent      : -121.7292, -120.8958, 45.8125, 46.64583  (xmin, xmax, ymin, ymax)
coord. ref. : lon/lat NAD83 (EPSG:4269) 
source      : memory 
names       : date2~08-11, date2~08-12, date2~08-13, date2~08-14, date2~08-15, date2~08-16, ... 
min values  :      10.188,       8.811,       6.811,       3.640,       1.833,       6.780, ... 
max values  :      29.842,      28.892,      27.123,      23.171,      21.858,      24.690, ...

You can convert a Raster\(^*\) object to a stars object using st_as_stars() (you will see a use case in Chapter 9.4.2).

(
tmax_PRISM_m8_y09_back_to_stars <- st_as_stars(tmax_PRISM_m8_y09_rb) 
)

stars object with 3 dimensions and 1 attribute
attribute(s):
          Min.  1st Qu. Median     Mean  3rd Qu.   Max.
layer.1  1.833 17.55575 21.483 22.03543 26.54275 39.707
dimension(s):
     from to     offset      delta refsys point values x/y
x       1 20   -121.729  0.0416667  NAD83    NA   NULL [x]
y       1 20    46.6458 -0.0416667  NAD83    NA   NULL [y]
band    1 10 2009-08-11     1 days   Date    NA   NULL

Notice that the original date values (stored in the date dimension) are recovered, but its dimension is now called just band.

You can do the same with a SpatRaster object.

(
tmax_PRISM_m8_y09_back_to_stars <- st_as_stars(tmax_PRISM_m8_y09_sr) 
)

stars object with 3 dimensions and 1 attribute
attribute(s):
         Min.  1st Qu. Median     Mean  3rd Qu.   Max.
values  1.833 17.55575 21.483 22.03543 26.54275 39.707
dimension(s):
     from to   offset      delta refsys point                            values
x       1 20 -121.729  0.0416667  NAD83    NA                              NULL
y       1 20  46.6458 -0.0416667  NAD83    NA                              NULL
band    1 10       NA         NA     NA    NA date2009-08-11,...,date2009-08-20
     x/y
x    [x]
y    [y]
band

Note that unlike the conversion from the RasterBrick object, the band dimension inherited values of the name dimension in tmax_PRISM_m8_y09_sr.