warp() is a wrapper of the gdalwarp command-line utility for
raster mosaicing, reprojection and warping
(see https://gdal.org/programs/gdalwarp.html).
The function can reproject to any supported spatial reference system (SRS).
It can also be used to crop, resample, and optionally write output to a
different raster format. See Details for a list of commonly used
processing options that can be passed as arguments to warp().
warp(src_files, dst_filename, t_srs, cl_arg = NULL, quiet = FALSE)Logical indicating success (invisible TRUE).
An error is raised if the operation fails.
Character vector of source file(s) to be reprojected.
Character string. Filename of the output raster.
Character string. Target spatial reference system. Usually an
EPSG code ("EPSG:#####") or a well known text (WKT) SRS definition.
If empty string "", the spatial reference of src_files[1] will be
used (see Note).
Optional character vector of command-line arguments to
gdalwarp in addition to -t_srs (see Details).
Logical scalar. If TRUE, a progress bar will not be
displayed. Defaults to FALSE.
Several processing options can be performed in one call to warp() by
passing the necessary command-line arguments. The following list describes
several commonly used arguments. Note that gdalwarp supports a large
number of arguments that enable a variety of different processing options.
Users are encouraged to review the original source documentation provided
by the GDAL project at the URL above for the full list.
-te <xmin> <ymin> <xmax> <ymax>
Georeferenced extents of output file to be created (in target SRS by
default).
-te_srs <srs_def>
SRS in which to interpret the coordinates given with -te
(if different than t_srs).
-tr <xres> <yres>
Output pixel resolution (in target georeferenced units).
-tap
(target aligned pixels) align the coordinates of the extent of the output
file to the values of the -tr, such that the aligned extent includes
the minimum extent. Alignment means that xmin / resx, ymin / resy,
xmax / resx and ymax / resy are integer values.
-ovr <level>|AUTO|AUTO-<n>|NONE
Specify which overview level of source files must be used. The default
choice, AUTO, will select the overview level whose resolution is the
closest to the target resolution. Specify an integer value (0-based,
i.e., 0=1st overview level) to select a particular level. Specify
AUTO-n where n is an integer greater or equal to 1, to select an
overview level below the AUTO one. Or specify NONE to force the base
resolution to be used (can be useful if overviews have been generated
with a low quality resampling method, and the warping is done using a
higher quality resampling method).
-wo <NAME>=<VALUE>
Set a warp option as described in the GDAL documentation for
GDALWarpOptions
Multiple -wo may be given. See also -multi below.
-ot <type>
Force the output raster bands to have a specific data type supported by
the format, which may be one of the following: Byte, Int8, UInt16,
Int16, UInt32, Int32, UInt64, Int64, Float32, Float64,
CInt16, CInt32, CFloat32 or CFloat64.
-r <resampling_method>
Resampling method to use. Available methods are: near (nearest
neighbour, the default), bilinear, cubic, cubicspline, lanczos,
average, rms (root mean square, GDAL >= 3.3), mode, max, min,
med, q1 (first quartile), q3 (third quartile), sum (GDAL >= 3.1).
-srcnodata "<value>[ <value>]..."
Set nodata masking values for input bands (different values can be
supplied for each band). If more than one value is supplied all values
should be quoted to keep them together as a single operating system
argument. Masked values will not be used in interpolation. Use a value of
None to ignore intrinsic nodata settings on the source dataset.
If -srcnodata is not explicitly set, but the source dataset has nodata
values, they will be taken into account by default.
-dstnodata "<value>[ <value>]..."
Set nodata values for output bands (different values can be supplied for
each band). If more than one value is supplied all values should be
quoted to keep them together as a single operating system argument. New
files will be initialized to this value and if possible the nodata value
will be recorded in the output file. Use a value of "None" to ensure
that nodata is not defined. If this argument is not used then nodata
values will be copied from the source dataset.
-wm <memory_in_mb>
Set the amount of memory that the warp API is allowed to use for caching.
The value is interpreted as being in megabytes if the value is <10000.
For values >=10000, this is interpreted as bytes. The warper will
total up the memory required to hold the input and output image arrays
and any auxiliary masking arrays and if they are larger than the
"warp memory" allowed it will subdivide the chunk into smaller chunks and
try again. If the -wm value is very small there is some extra overhead
in doing many small chunks so setting it larger is better but it is a
matter of diminishing returns.
-multi
Use multithreaded warping implementation. Two threads will be used to
process chunks of image and perform input/output operation
simultaneously. Note that computation is not multithreaded itself. To do
that, you can use the -wo NUM_THREADS=val/ALL_CPUS option, which can be
combined with -multi.
-of <format>
Set the output raster format. Will be guessed from the extension if not
specified. Use the short format name (e.g., "GTiff").
-co <NAME>=<VALUE>
Set one or more format specific creation options for the output dataset.
For example, the GeoTIFF driver supports creation options to control
compression, and whether the file should be tiled.
getCreationOptions() can be used to look up available creation options,
but the GDAL Raster drivers
documentation is the definitive reference for format specific options.
Multiple -co may be given, e.g.,
c("-co", "COMPRESS=LZW", "-co", "BIGTIFF=YES") -overwrite
Overwrite the target dataset if it already exists. Overwriting means
deleting and recreating the file from scratch. Note that if this option
is not specified and the output file already exists, it will be updated
in place.
The documentation for gdalwarp
describes additional command-line options related to spatial reference
systems, source nodata values, alpha bands, polygon cutlines as mask
including blending, and more.
Mosaicing into an existing output file is supported if the output file
already exists. The spatial extent of the existing file will not be
modified to accommodate new data, so you may have to remove it in that
case, or use the -overwrite option.
Command-line options are passed to warp() as a character vector. The
elements of the vector are the individual options followed by their
individual values, e.g.,
cl_arg = c("-tr", "30", "30", "-r", "bilinear"))
to set the target pixel resolution to 30 x 30 in target georeferenced units and use bilinear resampling.
GDALRaster-class, srs_to_wkt(), translate()
# reproject the elevation raster to NAD83 / CONUS Albers (EPSG:5070)
elev_file <- system.file("extdata/storml_elev.tif", package="gdalraster")
# command-line arguments for gdalwarp
# resample to 90-m resolution and keep pixels aligned:
args <- c("-tr", "90", "90", "-r", "cubic", "-tap")
# write to Erdas Imagine format (HFA) with compression:
args <- c(args, "-of", "HFA", "-co", "COMPRESSED=YES")
alb83_file <- file.path(tempdir(), "storml_elev_alb83.img")
warp(elev_file, alb83_file, t_srs="EPSG:5070", cl_arg = args)
ds <- new(GDALRaster, alb83_file)
ds$getDriverLongName()
ds$getProjectionRef()
ds$res()
ds$getStatistics(band=1, approx_ok=FALSE, force=TRUE)
ds$close()
deleteDataset(alb83_file)
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