st_warp: Warp (resample) grids in stars objects to a new grid,...

In stars: Spatiotemporal Arrays, Raster and Vector Data Cubes

Warp (resample) grids in stars objects to a new grid, possibly in an new coordinate reference system

Description

Warp (resample) grids in stars objects to a new grid, possibly in an new coordinate reference system

Usage

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",
  threshold = NA_real_
)

Arguments

src	object of class stars with source raster
dest	object of class stars with target raster geometry
...	ignored
crs	coordinate reference system for destination grid, only used when dest is missing
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 TRUE, use gdal's warp or warper, through gdal_utils
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; not setting this when use_gdal is TRUE leads to a warning
debug	logical; if TRUE, do not remove the temporary gdalwarp destination file, and print its name
method	character; see details for options; methods other than near only work when use_gdal=TRUE
threshold	numeric; distance threshold for warping curvilinear grids: new cells at distances larger than threshold are assigned NA values.

Details

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. 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.

Examples

geomatrix = system.file("tif/geomatrix.tif", package = "stars")
(x = read_stars(geomatrix))
new_crs = st_crs('OGC:CRS84')
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('OGC:CRS84') %>% 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)

stars documentation built on May 29, 2024, 8:59 a.m.