gdallocationinfo: Query raster files at points
In johnbaums/things: Mostly spatial things

Description Usage Arguments Value Examples

Return cell values for one or more raster files, at a given point or set of points. Requires that GDAL is installed and avilable to system (i.e. listed in the PATH environmental variable).

1	gdallocationinfo(srcfile, pts, simplify = TRUE, sp = FALSE)

`srcfile`	A character vector of file paths to the raster files to be queried.
`pts`	A `matrix`, `data.frame`, or `SpatialPoints*` object giving the x and y coordinates of a point (or points), given in the coordinate reference system of the rasters indicated at `srcfile`.
`simplify`	Logical. If `TRUE`, then if all files referred to in `srcfile` are single band rasters, the sampled values will be simplified to a matrix.
`sp`	Logical. If `TRUE`, a `SpatialPointsDataFrame` will be returned, otherwise a `data.frame` will be returned. If `pts` is a `SpatialPoints*` object and has a non-`NA` CRS, then if `sp` is `TRUE`, the returned object will have that same CRS assigned.

If only one file is queried, then a matrix is returned, with columns corresponding to bands of the file. If simplify is TRUE and all files are single band, the returned value will be a matrix with one column for each file, and rows giving the values of cells corresponding to the coordinates given by x and y. If simplify is FALSE, or if one or more files is multiband, the returned value is a list of matrices, with the columns of each matrix corresponding to the bands of the file. Further, if sp is TRUE, data will be returned as SpatialPointsDataFrames.

library(raster)
r <- raster(matrix(runif(1.6e7), ncol=4000))
r[sample(ncell(r), 10000000)] <- NA
writeRaster(r, f <- tempfile(fileext='.tif'))
file.info(f)
xy <- data.frame(x=runif(10000), y=runif(10000))

# Querying a single file at xy
vals <- gdallocationinfo(f, pts=xy)

# Querying multiple files (here identical) at xy:
vals2 <- gdallocationinfo(c(f, f, f), pts=xy)

# Returning as a SpatialPointsDataFrame
vals2 <- gdallocationinfo(c(f, f, f), pts=xy, sp=TRUE)