| 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. create2GDAL creates a GDAL data set from a SpatialGridDataFrame object, in particular to be able to save to GDAL driver formats that only permit copying rather than creation.
readGDAL(fname, offset, region.dim, output.dim, band, p4s=NULL, ..., half.cell=c(0.5, 0.5), silent = FALSE) asSGDF_GROD(x, offset, region.dim, output.dim, p4s=NULL, ..., half.cell=c(0.5,0.5)) writeGDAL(dataset, fname, drivername = "GTiff", type = "Float32", mvFlag = NA, options=NULL) create2GDAL(dataset, drivername = "GTiff", type = "Float32", mvFlag = NA, options=NULL) 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 |
band |
if missing, all bands are read |
p4s |
PROJ4 string defining CRS, if default (NULL), the value is read from the GDAL data set |
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
library(grid)
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], band=1)
summary(y)
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))
tf <- tempfile()
writeGDAL(erdas_spnad83, tf, drivername="GTiff", type="Byte", options=NULL)
all.equal(erdas_spnad83, readGDAL(tf))
writeGDAL(erdas_spnad83, tf, drivername="GTiff", type="Byte", options="INTERLEAVE=PIXEL")
all.equal(erdas_spnad83, readGDAL(tf))
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))
tf <- tempfile()
xx <- create2GDAL(erdas_spnad83, type="Byte")
xxx <- copyDataset(xx, driver="PNG")
saveDataset(xxx, tf)
GDAL.close(xx)
GDAL.close(xxx)
GDALinfo(tf)