readGDAL

From rgdal v0.3-7 by Roger Bivand

Read/write between GDAL grid maps and Spatial objects

The functions read or write GDAL grid maps. They will set the spatial reference system if available.

Keywords: spatial

Usage

readGDAL(fname, offset, region.dim, ..., half.cell=c(0.5, 0.5), silent = FALSE)
writeGDAL(dataset, fname, drivername = "GTiff", type = "Float32", mvFlag = NA)

Arguments

fname: file name of grid map
offset: Number of rows and columns from the origin (usually the upper left corner) to begin reading from; presently ordered (y,x) - this may change
region.dim: The number of rows and columns to read from the dataset; presently ordered (y,x) - this may change
half.cell: Used to adjust the intra-cell offset from corner to centre, usually as default, but may be set to c=(0,0) if needed; presently ordered (y,x) - this may change
silent: logical; if TRUE, comment is suppressed
...: arguments passed to either getRasterData, or getRasterTable, depending on rotation angles (see below); see the rgdal documentation for the available options (subsetting etc.)
dataset: object of class SpatialGridDataFrame-class or SpatialPixelsDataFrame-class
drivername: GDAL driver name
type: GDAL write data type (others than this default have not been tested)
mvFlag: missing value flag for output file

Value

read.GDAL returns the data in the file as a Spatial object.
Usually, GDAL maps will be north-south oriented, in which case the rgdal function getRasterData is used to read the data, and an object of class SpatialGridDataFrame-class is returned.
Some map formats supported by GDAL are not north-south oriented grids. If this is the case, readGDAL returns the data as a set of point data, being of class SpatialPointsDataFrame-class. If the points are on a 45 or 90 degree rotated grid, you can try to enforce gridding later on by e.g. using gridded(x)=TRUE.

Examples

x <- readGDAL(system.file("external/test.ag", package="sp")[1])
class(x)
image(x)
summary(x)
x@data[[1]][x@data[[1]] > 10000] <- NA
summary(x)
image(x)

x <- readGDAL(system.file("external/simple.ag", package="sp")[1])
class(x)
image(x)
summary(x)
y = readGDAL(system.file("pictures/Rlogo.jpg", package = "rgdal")[1])
summary(y)
spplot(y, zcol=1:3, names.attr=c("red","green","blue"), 
	col.regions=grey(0:100/100),
	main="example of three-layer (RGB) raster image", as.table=TRUE)
data(meuse.grid)
gridded(meuse.grid) = ~x+y
proj4string(meuse.grid) = CRS("+init=epsg:28992")
fn <- tempfile()
writeGDAL(meuse.grid["dist"], fn)
mg2 <- readGDAL(fn)
proj4string(mg2)
SP27GTIF <- readGDAL(system.file("pictures/SP27GTIF.TIF", package = "rgdal")[1])
summary(SP27GTIF)
image(SP27GTIF, col=grey(1:99/100))
cea <- readGDAL(system.file("pictures/cea.tif", package = "rgdal")[1])
summary(cea)
image(cea, col=grey(1:99/100))
erdas_spnad83 <- readGDAL(system.file("pictures/erdas_spnad83.tif", package = "rgdal")[1])
summary(erdas_spnad83)
image(erdas_spnad83, col=grey(1:99/100))

Documentation reproduced from package rgdal, version 0.3-7, License: GPL (version 2 or higher; see LICENSE)

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