warp: Warp individual scenes to a given projection

In loicdtx/VCF: Utilities for working with the Landsat based tree cover data

Description

This function allows single scenes to be warped to a given projection. No mosaicking is performed. The function can handle multiple NoData values and can output an alpha layer, which a warped layer containing the NoData values only.

Usage

warp(x, t_srs, nodata = NULL, filename, res = 30, method = "bilinear",
  alpha = FALSE, run = TRUE, ...)

Arguments

x	Character. The filename of the layer to be warped.
t_srs	character. proj4 expression of the output (filename) file.
nodata	numeric. Value that should not get interpolated in the resampling. Can take multiple values (i.e.: c(220, 210, 211)). No need to specify the nodata value if that one is included in the file header.
filename	character. filename of the output file, with full path.
res	numeric. output resolution.
method	character. resampling method. See http://www.gdal.org/gdalwarp.html
alpha	Logical. Should an alpha layer be created. Only makes sense in case multiple NoData values are provided.
run	logical. should the warping be executed. If set to false, a gdalwarp command string is generated, but not executed.
...	Character. Extra switches passed to gdalwarp, see http://www.gdal.org/gdalwarp.html. All arguments have to passed (including defaults) to be abble to use this ellipsis.

Details

Requires gdal to be installed on the system, and the the gdal binary folder should be added to the system path. On windows systems, gdal can be installed via FWTools, OSGeo4W or QGIS. Function behavior is quite different depending on whether single and multiple NoData are provided. gdalwarp, which is called via a system command does not support multiple NoData values, as a consequence the present function first aggregates all values provided in a single value and does the warping in a second stage.

Value

A character, or list of characters, the gdalwarp command(s). If you inted to copy/past it in a terminal, you can use print(), with quote=FALSE.

Author(s)

Loic Dutrieux

References

http://www.gdal.org/gdalwarp.html

Examples

## Not run: 
pr <- getPR('Belize')
pr <- pr$PR[1]
dir <- tempdir()
downloadPR(pr, year=2000, dir=dir)
unpackVCF(pr=pr, year=2000, searchDir=dir, dir=sprintf('%s/%s',dir,'extract/'))
x <- list.files(sprintf('%s/%s',dir,'extract/'), full.names=TRUE)
filename <- sprintf('%s.tif', rasterTmpFile())
warp(x=x, t_srs='+proj=laea +lat_0=-10 +lon_0=-70 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m +no_defs', nodata = c(200, 210, 211, 220), filename=filename)
a <- raster(filename)

# This function is intended to be applied to several scenes, as a way to prepare them before mosaicking
# The example below performs warping over three files and subsequently mosaic them

pr <- getPR('Belize')
dir <- tempdir()
downloadPR(pr, year=2000, dir=dir)
unpackVCF(pr=pr, year=2000, searchDir=dir, dir=sprintf('%s/%s',dir,'extract/'))
x <- list.files(sprintf('%s/%s',dir,'extract/'), full.names=TRUE)

wrap <- function(x) {
  filename <- filename <- sprintf('%s_warp.tif', x)
  w <- warp(x=x, t_srs='+proj=laea +lat_0=-10 +lon_0=-70 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m +no_defs', nodata = c(200, 210, 211, 220), filename=filename)
  return(w)
}

mclapply(X=x, FUN=wrap, mc.cores=3)

x2 <- list.files(sprintf('%s/%s',dir,'extract/'), pattern=glob2rx('*warp*'), full.names=TRUE)

x3 <- lapply(X=x2, FUN=raster)
x3$fun <- mean
x3$filename <- sprintf('%s/%s',dir,'extract/mosaic_belize.tif')

do.call(raster::mosaic, x3)
plot(r <- raster(x3$filename))


## End(Not run)

loicdtx/VCF documentation built on May 21, 2019, 7:37 a.m.