wondering why terra::roll() will not match window_time()

[zackarno]

I'm probably misunderstanding something. But I cannot make terra::rolll() match the results of window_time() which i thought would be possible.

Below is a reprex where I try 2 methods for window_time() and then play with the parameters in terra::roll() in several different ways. Nonetheless I can't get them to match up.

library(terra)
#> terra 1.7.78
library(stars)
#> Loading required package: abind
#> Loading required package: sf
#> Warning: package 'sf' was built under R version 4.4.1
#> Linking to GEOS 3.11.0, GDAL 3.5.3, PROJ 9.1.0; sf_use_s2() is TRUE
library(gdalcubes)
#> 
#> Attaching package: 'gdalcubes'
#> The following objects are masked from 'package:terra':
#> 
#>     animate, crop, size

# create image collection from example Landsat data only 
# if not already done in other examples
if (!file.exists(file.path(tempdir(), "L8.db"))) {
  L8_files <- list.files(system.file("L8NY18", package = "gdalcubes"),
                         ".TIF", recursive = TRUE, full.names = TRUE)
  create_image_collection(L8_files, "L8_L1TP", file.path(tempdir(), "L8.db"), quiet = TRUE) 
}

L8.col = image_collection(file.path(tempdir(), "L8.db"))
v = cube_view(extent=list(left=388941.2, right=766552.4, 
                          bottom=4345299, top=4744931, t0="2018-01", t1="2018-07"),
              srs="EPSG:32618", nx = 400, dt="P1M")
L8.cube = raster_cube(L8.col, v) 
L8.nir = select_bands(L8.cube, c("B05"))

# first w/ mean expr
L8.nir.rollmean_expr = window_time(L8.nir, window = c(1,1), expr = "mean(B05)")  

# then with kernel
L8.nir.rollmean_kernel = window_time(L8.nir, window = c(1,1),kernel = rep(1/3,3))

# convert to terra raster so i can see the values better
window_result_expr <- terra::rast(stars::st_as_stars(L8.nir.rollmean_expr))
#> Warning in CPL_read_gdal(as.character(x), as.character(options),
#> as.character(driver), : GDAL Message 1: The dataset has several variables that
#> could be identified as vector fields, but not all share the same primary
#> dimension. Consequently they will be ignored.
window_result_kernel <- terra::rast(stars::st_as_stars(L8.nir.rollmean_kernel))
#> Warning in CPL_read_gdal(as.character(x), as.character(options),
#> as.character(driver), : GDAL Message 1: The dataset has several variables that
#> could be identified as vector fields, but not all share the same primary
#> dimension. Consequently they will be ignored.


# take original cube and convert to terra
r_from_cube <- terra::rast(stars::st_as_stars(L8.cube))
#> Warning in CPL_read_gdal(as.character(x), as.character(options),
#> as.character(driver), : GDAL Message 1: The dataset has several variables that
#> could be identified as vector fields, but not all share the same primary
#> dimension. Consequently they will be ignored.
r_from_cube
#> class       : SpatRaster 
#> dimensions  : 423, 400, 7  (nrow, ncol, nlyr)
#> resolution  : 944.028, 944.7565  (x, y)
#> extent      : 388941.2, 766552.4, 4345299, 4744931  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 18N (EPSG:32618) 
#> source(s)   : memory
#> names       : time2~01-01, time2~02-01, time2~03-01, time2~04-01, time2~05-01, time2~06-01, ... 
#> min values  :        7889,         NaN,        8616,        9259,        9782,        9375, ... 
#> max values  :       21454,         NaN,       31587,       50520,       40355,       47991, ... 
#> time (raw)  : 1 to 7

terra_result_na_T <- terra::roll(
  x=r_from_cube,
  n=3, 
  fun = "mean",
  na.rm=T
)
terra_result_na_T_circular <- terra::roll(
  x=r_from_cube,
  n=3, 
  fun = "mean",
  na.rm=T, 
  circular =T
)
terra_result_na_F <- terra::roll(
  x=r_from_cube,
  n=3, 
  fun = "mean",na.rm=F
)
terra_result_na_F_circular <- terra::roll(
  x=r_from_cube,
  n=3, 
  fun = "mean",na.rm=F, circular=T
)

window_result_expr
#> class       : SpatRaster 
#> dimensions  : 423, 400, 7  (nrow, ncol, nlyr)
#> resolution  : 944.028, 944.7565  (x, y)
#> extent      : 388941.2, 766552.4, 4345299, 4744931  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 18N (EPSG:32618) 
#> source(s)   : memory
#> names       : time2~01-01, time2~02-01, time2~03-01, time2~04-01, time2~05-01, time2~06-01, ... 
#> min values  :        5278,        5278,        5383,        5383,        5564,        5510, ... 
#> max values  :       27253,       33477,       57497,       45797,       45797,       48476, ... 
#> time (raw)  : 1 to 7
window_result_kernel
#> class       : SpatRaster 
#> dimensions  : 423, 400, 7  (nrow, ncol, nlyr)
#> resolution  : 944.028, 944.7565  (x, y)
#> extent      : 388941.2, 766552.4, 4345299, 4744931  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 18N (EPSG:32618) 
#> source(s)   : memory
#> names       : time2~01-01, time2~02-01, time2~03-01, time2~04-01, time2~05-01, time2~06-01, ... 
#> min values  :         NaN,         NaN,         NaN,        6395,    6580.333,    6528.333, ... 
#> max values  :         NaN,         NaN,         NaN,       38198,   38943.333,   35322.000, ... 
#> time (raw)  : 1 to 7
terra_result_na_T
#> class       : SpatRaster 
#> dimensions  : 423, 400, 7  (nrow, ncol, nlyr)
#> resolution  : 944.028, 944.7565  (x, y)
#> extent      : 388941.2, 766552.4, 4345299, 4744931  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 18N (EPSG:32618) 
#> source(s)   : memory
#> names       : time2~01-01, time2~02-01, time2~03-01, time2~04-01, time2~05-01, time2~06-01, ... 
#> min values  :        7889,        7889,        8829,      8829.0,      9259.0,        9394, ... 
#> max values  :       21454,       31587,       50520,     36977.5,     36977.5,       39473, ... 
#> time (raw)  : 1 to 7
terra_result_na_T_circular
#> class       : SpatRaster 
#> dimensions  : 423, 400, 7  (nrow, ncol, nlyr)
#> resolution  : 944.028, 944.7565  (x, y)
#> extent      : 388941.2, 766552.4, 4345299, 4744931  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 18N (EPSG:32618) 
#> source(s)   : memory
#> names       : time2~01-01, time2~02-01, time2~03-01, time2~04-01, time2~05-01, time2~06-01, ... 
#> min values  :        7889,        7889,        8829,      8829.0,      9259.0,        9394, ... 
#> max values  :       20388,       31587,       50520,     36977.5,     36977.5,       39473, ... 
#> time (raw)  : 1 to 7
terra_result_na_F
#> class       : SpatRaster 
#> dimensions  : 423, 400, 7  (nrow, ncol, nlyr)
#> resolution  : 944.028, 944.7565  (x, y)
#> extent      : 388941.2, 766552.4, 4345299, 4744931  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 18N (EPSG:32618) 
#> source(s)   : memory
#> names       : time2~01-01, time2~02-01, time2~03-01, time2~04-01, time2~05-01, time2~06-01, ... 
#> min values  :         NaN,         NaN,         NaN,    9978.333,    9861.333,    10357.33, ... 
#> max values  :         NaN,         NaN,         NaN,   32611.000,   32742.333,    31030.00, ... 
#> time (raw)  : 1 to 7
terra_result_na_F_circular
#> class       : SpatRaster 
#> dimensions  : 423, 400, 7  (nrow, ncol, nlyr)
#> resolution  : 944.028, 944.7565  (x, y)
#> extent      : 388941.2, 766552.4, 4345299, 4744931  (xmin, xmax, ymin, ymax)
#> coord. ref. : WGS 84 / UTM zone 18N (EPSG:32618) 
#> source(s)   : memory
#> names       : time2~01-01, time2~02-01, time2~03-01, time2~04-01, time2~05-01, time2~06-01, ... 
#> min values  :         NaN,         NaN,         NaN,    9978.333,    9861.333,    10357.33, ... 
#> max values  :         NaN,         NaN,         NaN,   32611.000,   32742.333,    31030.00, ... 
#> time (raw)  : 1 to 7

^{Created on 2024-10-03 with reprex v2.1.0}