readAsciiGrid {maptools} | R Documentation

## read/write to/from (ESRI) asciigrid format

### Description

read/write to/from ESRI asciigrid format; a fuzz factor has been added to `writeAsciiGrid` to force cell resolution to equality if the difference is less than the square root of machine precision

### Usage

    readAsciiGrid(fname, as.image = FALSE, plot.image = FALSE,
     colname = basename(fname), proj4string = CRS(as.character(NA)),
     dec=options()$OutDec)
    writeAsciiGrid(x, fname, attr = 1, na.value = -9999, dec=options()$OutDec, ...)

### Arguments

`fname` | file name
`as.image` | logical; if TRUE, a list is returned, ready to be shown with the `image` command; if FALSE an object of class SpatialGridDataFrame-class is returned
`plot.image` | logical; if TRUE, an image of the map is plotted
`colname` | alternative name for data column if not file basename
`proj4string` | A CRS object setting the projection arguments of the Spatial Grid returned
`dec` | decimal point character. This should be a character string containing just one single-byte character — see note below.
`x` | object of class SpatialGridDataFrame
`attr` | attribute column; if missing, the first column is taken; a name or a column number may be given
`na.value` | numeric; value given to missing valued cells in the resulting map
`...` | arguments passed to write.table, which is used to write the numeric data

### Value

`readAsciiGrid` returns the grid map read; either as an object of class SpatialGridDataFrame-class or, if as.image is TRUE, as list with components `x`, `y` and `z`.

### Note

In ArcGIS 8, it was not in general necessary to set the `dec` argument; it is not necessary in a mixed environment with ArcView 3.2 (R writes and ArcView reads "."), but inter-operation with ArcGIS 9 requires care because the defaults used by ArcGIS seem to be misleading, and it may be necessary to override what appear to be platform defaults by setting the argument.

### Author(s)

Edzer Pebesma, edzer.pebesma@uni-muenster.de

### See Also

`image`, `image`

### Examples

    x <- readAsciiGrid(system.file("grids/test.ag", package="maptools")[1])
    summary(x)
    image(x)
    xp <- as(x, "SpatialPixelsDataFrame")
    abline(h=332000, lwd=3)
    xpS <- xp[coordinates(xp)[,2] < 332000,]
    summary(xpS)
    xS <- as(xpS, "SpatialGridDataFrame")
    summary(xS)
    tmpfl <- paste(tempdir(), "testS.ag", sep="/")
    writeAsciiGrid(xS, tmpfl)
    axS <- readAsciiGrid(tmpfl)
    opar <- par(mfrow=c(1,2))
    image(xS, main="before export")
    image(axS, main="after import")
    par(opar)
    unlink(tmpfl)

[Package maptools version 0.9-2 Index]