return the cell index corresponding to the location of a set of points
Source:R/stars.R
st_cells.RdIf the object has been cropped without normalization, then the indices return
are relative to the original uncropped extent. See st_crop
Examples
set.seed(1345)
st_bbox(L7_ETMs) |>
st_as_sfc() |>
st_sample(10) -> pts
(x <- st_cells(L7_ETMs, pts))
#> [1] 102496 112324 74862 56976 112862 105242 75593 11784 91245 63885
# get the pixel values (first band only):
st_as_stars(L7_ETMs)[[1]][x]
#> [1] 92 92 89 76 67 94 77 98 113 56
# get pixel values for all bands:
st_as_stars(L7_ETMs) |> split() |> sapply(`[`, x)
#> X1 X2 X3 X4 X5 X6
#> [1,] 92 81 60 14 14 11
#> [2,] 92 83 59 13 13 12
#> [3,] 89 83 88 66 113 92
#> [4,] 76 63 66 61 108 78
#> [5,] 67 55 50 65 69 38
#> [6,] 94 81 92 60 125 105
#> [7,] 77 63 65 58 114 93
#> [8,] 98 85 88 57 93 80
#> [9,] 113 98 104 66 110 94
#> [10,] 56 40 27 68 50 24
# compare with st_extract():
st_as_stars(L7_ETMs) |> split() |> st_extract(pts)
#> Simple feature collection with 10 features and 6 fields
#> Geometry type: POINT
#> Dimension: XY
#> Bounding box: xmin: 289267.4 ymin: 9111549 xmax: 297166.8 ymax: 9119794
#> Projected CRS: SIRGAS 2000 / UTM zone 25S
#> X1 X2 X3 X4 X5 X6 geometry
#> 1 92 81 60 14 14 11 POINT (295582.2 9112406)
#> 2 92 83 59 13 13 12 POINT (297166.8 9111599)
#> 3 89 83 88 66 113 92 POINT (293775.8 9114659)
#> 4 76 63 66 61 108 78 POINT (291294.7 9116093)
#> 5 67 55 50 65 69 38 POINT (292609.8 9111549)
#> 6 94 81 92 60 125 105 POINT (294276.2 9112159)
#> 7 77 63 65 58 114 93 POINT (294731 9114598)
#> 8 98 85 88 57 93 80 POINT (296360.6 9119794)
#> 9 113 98 104 66 110 94 POINT (293206.5 9113313)
#> 10 56 40 27 68 50 24 POINT (289267.4 9115521)