readGDAL {rgdal} | R Documentation |
The functions read or write GDAL grid maps. They will set the spatial reference system if available. GDALinfo
reports the size and other parameters of the dataset.
readGDAL(fname, offset, region.dim, output.dim, ..., half.cell=c(0.5, 0.5), silent = FALSE) asSGDF_GROD(x, offset, region.dim, output.dim, ..., half.cell=c(0.5,0.5)) writeGDAL(dataset, fname, drivername = "GTiff", type = "Float32", mvFlag = NA, options="" ) GDALinfo(fname)
fname |
file name of grid map |
x |
A GDALReadOnlyDataset object |
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 |
output.dim |
The number of rows and columns to return in the created object using GDAL's method to take care of image decimation / replication; 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 |
options |
driver-specific options to be passed to the GDAL driver |
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
.
Edzer J. Pebesma, Roger Bivand
as.image.SpatialGridDataFrame
, image
, readAsciiGrid
GDALinfo(system.file("external/test.ag", package="sp")[1]) 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], output.dim=c(100,100)) summary(SP27GTIF) image(SP27GTIF, col=grey(1:99/100)) GDALinfo(system.file("pictures/cea.tif", package = "rgdal")[1]) cea <- readGDAL(system.file("pictures/cea.tif", package = "rgdal")[1], output.dim=c(100,100)) summary(cea) image(cea, col=grey(1:99/100)) erdas_spnad83 <- readGDAL(system.file("pictures/erdas_spnad83.tif", package = "rgdal")[1], output.dim=c(100,100)) summary(erdas_spnad83) image(erdas_spnad83, col=grey(1:99/100)) x <- GDAL.open(system.file("pictures/erdas_spnad83.tif", package = "rgdal")[1]) erdas_spnad83 <- asSGDF_GROD(x, output.dim=c(100,100)) GDAL.close(x) summary(erdas_spnad83) image(erdas_spnad83, col=grey(1:99/100))