Warp (resample) grids in stars objects to a new grid, possibly in an new coordinate reference system
Warp (resample) grids in stars objects to a new grid, possibly in an new coordinate reference system
st_warp( src, dest, ..., crs = NA_crs_, cellsize = NA_real_, segments = 100, use_gdal = FALSE, options = character(0), no_data_value = NA_real_, debug = FALSE, method = "near" )
src |
object of class |
dest |
object of class |
... |
ignored |
crs |
coordinate reference system for destination grid, only used when |
cellsize |
length 1 or 2 numeric; cellsize in target coordinate reference system units |
segments |
(total) number of segments for segmentizing the bounding box before transforming to the new crs |
use_gdal |
logical; if |
options |
character vector with options, passed on to gdalwarp |
no_data_value |
value used by gdalwarp for no_data (NA) when writing to temporary file |
debug |
logical; if |
method |
character; see details for options; methods other than |
method should be one of near, bilinear, cubic, cubicspline, lanczos, average, mode, max, min, med, q1 or q3; see https://github.com/r-spatial/stars/issues/109
For gridded spatial data (dimensions x and y), see figure; the existing grid is transformed into a regular grid defined by dest, possibly in a new coordinate reference system. If dest is not specified, but crs is, the procedure used to choose a target grid is similar to that of projectRaster (currently only with method='ngb'). This entails: (i) the envelope (bounding box polygon) is transformed into the new crs, possibly after segmentation (red box); (ii) a grid is formed in this new crs, touching the transformed envelope on its East and North side, with (if cellsize is not given) a cellsize similar to the cell size of src, with an extent that at least covers x; (iii) for each cell center of this new grid, the matching grid cell of x is used; if there is no match, an NA value is used.
geomatrix = system.file("tif/geomatrix.tif", package = "stars")
(x = read_stars(geomatrix))
new_crs = st_crs(4326)
y = st_warp(x, crs = new_crs)
plot(st_transform(st_as_sfc(st_bbox(x)), new_crs), col = NA, border = 'red')
plot(st_as_sfc(y, as_points=FALSE), col = NA, border = 'green', axes = TRUE, add = TRUE)
image(y, add = TRUE, nbreaks = 6)
plot(st_as_sfc(y, as_points=TRUE), pch=3, cex=.5, col = 'blue', add = TRUE)
plot(st_transform(st_as_sfc(x, as_points=FALSE), new_crs), add = TRUE)
# warp 0-360 raster to -180-180 raster:
r = read_stars(system.file("nc/reduced.nc", package = "stars"))
r %>% st_set_crs(4326) %>% st_warp(st_as_stars(st_bbox(), dx = 2)) -> s
plot(r, axes = TRUE) # no CRS set, so no degree symbols in labels
plot(s, axes = TRUE)
# downsample raster (90 to 270 m)
r = read_stars(system.file("tif/olinda_dem_utm25s.tif", package = "stars"))
r270 = st_as_stars(st_bbox(r), dx = 270)
r270 = st_warp(r, r270)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.