readGDAL {rgdal} | R Documentation

## Read/write between GDAL grid maps and Spatial objects

### Description

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

### Usage

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

### 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
`options` | driver-specific options to be passed to the GDAL driver

### 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`.

### Author(s)

Edzer J. Pebesma, e.pebesma@geo.uu.nl

### See Also

`as.image.SpatialGridDataFrame`, `image`, `readAsciiGrid`

### 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))

[Package rgdal version 0.4-4 Index]