R: ESRI ASCII Raster File Import And Export

read.asc {SDMTools} | R Documentation

## ESRI ASCII Raster File Import And Export

### Description

`read.asc` and `read.asc.gz` reads ESRI ArcInfo ASCII raster file either uncompressed or compressed using gzip.
`write.asc` and `write.asc.gz` writes an asc object to a ESRI ArcInfo ASCII raster file. The output can be either compressed or uncompressed.
These functions are faster methods based on the adehabitat import.asc and export.asc.
`write.asc2` and `write.asc2.gz` are even faster implementations but have less error checking.
`image.asc` and `print.asc` are generic methods associated with plotting & summarizing data of class 'asc'; they were modified from adehabitat package.

### Usage

    read.asc(file, gz = FALSE)

    read.asc.gz(file)

    write.asc(x, file, gz = FALSE)

    write.asc.gz(x, file)

    write.asc2(x, file, sigdig = 0, gz = FALSE)

    write.asc2.gz(x, file, sigdig = 0)

    ## S3 method for class 'asc'
    image(x, col = gray((240:1)/256), clfac = NULL, ...)

    ## S3 method for class 'asc'
    print(x, ...)

### Arguments

`file` | a character string representing the filename of the input/output file. The file extension should always be '.asc'.
`gz` | defines if the object is or should be compressed using gzip
`x` | an object of class 'asc' as defined in the adehabitat package
`sigdig` | is the number of significant digits to write when creating the ascii grid file
`col` | for maps of type `"numeric"`, the colors to be used (see `help(par)`)
`clfac` | for maps of type `"factor"`, a character vector giving the names of colors for each level of the factor (see `help(colasc)`)
`...` | additional arguments to be passed to the generic function `image` or `print`

### Details

Implements a faster version of import.asc or export.asc from the adehabitat package. In addition, files can be read in and written to in gzip compressed format.
Generic methods of print and image were modified from adehabitat. Further details of them are found there.

### Value

Returns a raster matrix of the class 'asc' defined in the adehabitat package with the following attributes:

`xll` | the x coordinate of the center of the lower left pixel of the map
`yll` | the y coordinate of the center of the lower left pixel of the map
`cellsize` | the size of a pixel on the studied map
`type` | either 'numeric' or 'factor'
`levels` | if type = 'factor', the levels of the factor.

### Author(s)

Jeremy VanDerWal jjvanderwal@gmail.com

### Examples

    #create a simple object of class 'asc'
    tasc = as.asc(matrix(rep(x=1:10, times=1000),nr=100)); print(tasc)

    #write out the raster grid file
    write.asc(tasc,'t.raster.asc')
    write.asc.gz(tasc,'t.raster.asc') #actually save file name as t.raster.asc.gz

    #read in the raster grid files
    tasc2 = read.asc('t.raster.asc')
    tasc3 = read.asc.gz('t.raster.asc.gz')

    #remove the temporary raster
    unlink(c('t.raster.asc','t.raster.asc.gz'))

[Package SDMTools version 1.1-221.2 Index]