GDALReadOnlyDataset-class {rgdal} | R Documentation

## Class "GDALReadOnlyDataset"

### Description

`GDALReadOnlyDataset` is the base class for a GDAL Dataset classes. Only read operations are supported. Both `GDALDataset` and `GDALTransientDataset` inherit these read operations while providing additional write operations (see `GDALDataset-class`). `GDALReadOnlyDataset-class` inherits from `GDALMajorObject-class`.

### Usage

    GDAL.close(dataset)
    GDAL.open(filename)
    getDriver(dataset)
    displayDataset(x, offset = c(0, 0), region.dim = dim(x),
                               reduction = 1, band = NULL, col = NULL,
                               max.dim = 500, ...)
    getColorTable(dataset, band = 1)
    getGeoTransFunc(dataset)

### Arguments

`dataset` | An object inheriting from class 'GDALReadOnlyDataset'
`filename` | A string giving the file to read from
`x` | An object inheriting from class 'GDALReadOnlyDataset'
`offset` | Number of rows and columns from the origin (usually the upper left corner) to begin reading from
`region.dim` | The number of rows and columns to read from the dataset
`reduction` | scaling parameter for region.dim
`band` | The band number (1-based) to read from
`col` | a vector of colours or a colour function such as rainbow
`max.dim` | another scaling parameter
`...` | other plotting parameters passed through
`` |
`` |

### Details

`GDAL.open` and `GDAL.close` are shorter versions of `new("GDALReadOnlyDataset", ...)` and `closeDataset()`. Because `GDAL.close` through `closeDataset()` uses the finalization mechanism to destroy the handles to the dataset and its driver, messages such as:

"Closing GDAL dataset handle 0x8ff7900... destroyed ... done."

may appear when `GDAL.close` is run, or at some later stage. `getDriver` returns an object inheriting from class 'GDALDriver'. `displayDataset` and its use in `plot` for a pixmap object to produce a plot of the dataset, returning a pixmap object. `getColorTable` returns the dataset colour table (currently does not support RGB imaging). `getGeoTransFunc` returns a warping function.

### Objects from the Class

Objects can be created by calls of the form `new("GDALReadOnlyDataset", filename, handle)`. ~~ describe objects here ~~

### Slots

`handle`:
  Object of class `"externalptr", from class "GDALMajorObject"` ~~

### Extends

Class `"GDALMajorObject"`, directly.

### Methods

closeDataset
  `signature(dataset = "GDALReadOnlyDataset")`: ...
dim
  `signature(x = "GDALReadOnlyDataset")`: ...
initialize
  `signature(.Object = "GDALReadOnlyDataset")`: ...

### Author(s)

Timothy H. Keitt, modified by Roger Bivand

### References

http://keittlab.bio.sunysb.edu/R/GDAL/, http://www.remotesensing.org/gdal/

### See Also

See also `GDALDriver-class`, `GDALDataset-class`, `GDALTransientDataset-class`.

### Examples

    logo <- system.file("pictures/logo.jpg", package="rgdal")[1]
    x <- new("GDALReadOnlyDataset", logo)
    dim(x)
    plot(density(getRasterTable(x)$band1))
    displayDataset(x)
    displayDataset(x, col=function(x){rev(cm.colors(x))})
    im <- displayDataset(x, col=function(x){rev(cm.colors(x))}, reset.par=FALSE)
    contour(1:attr(im, "size")[2], 1:attr(im, "size")[1],
     t(attr(im, "index"))[,attr(im, "size")[1]:1], nlevels = 1,
     levels = 100, col = 'black', add = TRUE)
    GDAL.close(x)
    logo <- system.file("pictures/Rlogo.jpg", package="rgdal")[1]
    x <- new("GDALReadOnlyDataset", logo)
    dim(x)
    displayDataset(x)
    GDAL.close(x)

[Package rgdal version 0.4-4 Index]