readAsciiGrid: 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, ...)

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.

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

Author

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

Examples

Run this code

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)