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get dimensions from stars object

Source: R/dimensions.R
st_dimensions.Rd

get dimensions from stars object

Usage

st_dimensions(.x, ...)

# S3 method for stars
st_dimensions(.x, ...)

st_dimensions(x) <- value

# S3 method for stars
st_dimensions(x) <- value

# S3 method for stars_proxy
st_dimensions(x) <- value

# S3 method for list
st_dimensions(x) <- value

# S3 method for array
st_dimensions(.x, ...)

# S3 method for default
st_dimensions(
  .x,
  ...,
  .raster,
  affine = c(0, 0),
  cell_midpoints = FALSE,
  point = FALSE
)

st_set_dimensions(
  .x,
  which,
  values = NULL,
  point = NULL,
  names = NULL,
  xy,
  ...
)

st_get_dimension_values(.x, which, ..., where = NA, max = FALSE, center = NA)

Arguments

.x

object to retrieve dimensions information from

...

further arguments

x

object of class dimensions

value

new object of class dimensions, with matching dimensions

.raster

length 2 character array with names (if any) of the raster dimensions

affine

numeric; specify parameters of the affine transformation

cell_midpoints

logical; if TRUE AND the dimension values are strictly regular, the values are interpreted as the cell midpoint values rather than the cell offset values when calculating offset (i.e., the half-cell-size correction is applied); can have a value for each dimension, or else is recycled

point

logical; does the pixel value (measure) refer to a point (location) value or to an pixel (area) summary value?

which

integer or character; index or name of the dimension to be changed

values

values for this dimension (e.g. sfc list-column), or length-1 dimensions object; setting special value NULL removes dimension values, for instance to remove curvilinear raster coordinates

names

character; vector with new names for all dimensions, or with the single new name for the dimension indicated by which

xy

length-2 character vector; (new) names for the x and y raster dimensions

where

character, one of 'start', 'center' or 'end'. Set to NA (default) to ignore and use max and center explictly. This argument provides a convenient alternative to setting max and center.

max

logical; if TRUE return the end, rather than the beginning of an interval

center

logical; if TRUE return the center of an interval; if NA return the center for raster dimensions, and the start of intervals in other cases

Value

the dimensions attribute of x, of class dimensions

Details

dimensions can be specified in two ways. The simplest is to pass a vector with numeric values for a numeric dimension, or character values for a categorical dimension. Parameter cell_midpoints is used to specify whether numeric values refer to the offset (start) of a dimension interval (default), or to the center; the center case is only available for regular dimensions. For rectilinear numeric dimensions, one can specify either a vector with cell borders (start values), or a data.frame with two columns named "start" and "end", with the respective interval start and end values. In the first case, the end values are computed from the start values by assuming the last two intervals have equal width.

Examples

x = read_stars(system.file("tif/L7_ETMs.tif", package = "stars"))
# Landsat 7 ETM+ band semantics: https://landsat.gsfc.nasa.gov/the-enhanced-thematic-mapper-plus/
# set bands to values 1,2,3,4,5,7:
(x1 = st_set_dimensions(x, "band", values = c(1,2,3,4,5,7), names = "band_number", point = TRUE))
#> stars object with 3 dimensions and 1 attribute
#> attribute(s):
#>              Min. 1st Qu. Median     Mean 3rd Qu. Max.
#> L7_ETMs.tif     1      54     69 68.91242      86  255
#> dimension(s):
#>             from  to  offset delta                     refsys point  values x/y
#> x              1 349  288776  28.5 SIRGAS 2000 / UTM zone 25S FALSE    NULL [x]
#> y              1 352 9120761 -28.5 SIRGAS 2000 / UTM zone 25S FALSE    NULL [y]
#> band_number    1   6      NA    NA                         NA  TRUE 1,...,7    
# set band values as bandwidth
rbind(c(0.45,0.515), c(0.525,0.605), c(0.63,0.69), c(0.775,0.90), c(1.55,1.75), c(2.08,2.35)) %>%
  units::set_units("um") -> bw # or: units::set_units(µm) -> bw
# set bandwidth midpoint:
(x2 = st_set_dimensions(x, "band", values = 0.5 * (bw[,1]+bw[,2]), 
   names = "bandwidth_midpoint", point = TRUE))
#> stars object with 3 dimensions and 1 attribute
#> attribute(s):
#>              Min. 1st Qu. Median     Mean 3rd Qu. Max.
#> L7_ETMs.tif     1      54     69 68.91242      86  255
#> dimension(s):
#>                    from  to  offset delta                     refsys point
#> x                     1 349  288776  28.5 SIRGAS 2000 / UTM zone 25S FALSE
#> y                     1 352 9120761 -28.5 SIRGAS 2000 / UTM zone 25S FALSE
#> bandwidth_midpoint    1   6      NA    NA                    udunits  TRUE
#>                                        values x/y
#> x                                        NULL [x]
#> y                                        NULL [y]
#> bandwidth_midpoint 0.4825 [um],...,2.215 [um]    
# set bandwidth intervals:
(x3 = st_set_dimensions(x, "band", values = make_intervals(bw), names = "bandwidth"))
#> stars object with 3 dimensions and 1 attribute
#> attribute(s):
#>              Min. 1st Qu. Median     Mean 3rd Qu. Max.
#> L7_ETMs.tif     1      54     69 68.91242      86  255
#> dimension(s):
#>           from  to  offset delta                     refsys point
#> x            1 349  288776  28.5 SIRGAS 2000 / UTM zone 25S FALSE
#> y            1 352 9120761 -28.5 SIRGAS 2000 / UTM zone 25S FALSE
#> bandwidth    1   6      NA    NA                    udunits    NA
#>                                           values x/y
#> x                                           NULL [x]
#> y                                           NULL [y]
#> bandwidth [0.45,0.515) [um],...,[2.08,2.35) [um]    
m = matrix(1:20, nrow = 5, ncol = 4)
dim(m) = c(x = 5, y = 4) # named dim
(s = st_as_stars(m))
#> stars object with 2 dimensions and 1 attribute
#> attribute(s):
#>     Min. 1st Qu. Median Mean 3rd Qu. Max.
#> A1     1    5.75   10.5 10.5   15.25   20
#> dimension(s):
#>   from to offset delta point x/y
#> x    1  5      0     1 FALSE [x]
#> y    1  4      0     1 FALSE [y]
st_get_dimension_values(s, 'x', where = "start")
#> [1] 0 1 2 3 4
st_get_dimension_values(s, 'x', center = FALSE)
#> [1] 0 1 2 3 4
st_get_dimension_values(s, 'x', where = "center")
#> [1] 0.5 1.5 2.5 3.5 4.5
st_get_dimension_values(s, 'x', center = TRUE)
#> [1] 0.5 1.5 2.5 3.5 4.5
st_get_dimension_values(s, 'x', where = "end")
#> [1] 1 2 3 4 5
st_get_dimension_values(s, 'x', max = TRUE)
#> [1] 1 2 3 4 5