1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
|
\name{read.ENVI & write.ENVI}
\alias{read.ENVI}
\alias{write.ENVI}
\title{Read and Write Binary Data in ENVI Format}
\description{Read and write binary data in ENVI format, which is supported by
most GIS software.}
\usage{
X=read.ENVI(filename, headerfile=paste(filename, ".hdr", sep=""))
write.ENVI (X, filename, interleave = c("bsq", "bil", "bip"))
}
\arguments{
\item{X}{data to be saved in ENVI file. Can be a matrix or 3D array.}
\item{filename}{character string with name of the file (connection)}
\item{headerfile}{optional character string with name of the header file}
\item{interleave}{optional character string specifying interleave to be used}
}
\details{
ENVI binary files use a generalized raster data format that consists of two
parts:
\itemize{
\item binary file - flat binary file equivalent to memory dump, as produced by
\code{\link{writeBin}} in R or \code{fwrite} in C/C++.
\item header file - small text (ASCII) file containing the metadata
associated with the binary file. This file can contain the following
fields, followed by equal sign and a variable:
\itemize{
\item \code{samples} - number of columns \cr
\item \code{lines} - number of rows \cr
\item \code{bands} - number of bands (channels, planes) \cr
\item \code{data type} - following types are supported:
\itemize{
\item 1 - 1-byte unsigned integer
\item 2 - 2-byte signed integer
\item 3 - 4-byte signed integer
\item 4 - 4-byte float
\item 5 - 8-byte double
\item 9 - 2x8-byte complex number made up from 2 doubles
\item 12 - 2-byte unsigned integer
}
\item \code{header offset} - number of bytes to skip before
raster data starts in binary file.
\item \code{interleave} - Permutations of dimensions in binary data:
\itemize{
\item \code{BSQ} - Band Sequential (X[col,row,band])
\item \code{BIL} - Band Interleave by Line (X[col,band,row])
\item \code{BIP} - Band Interleave by Pixel (X[band,col,row])
}
\item \code{byte order} - the endian-ness of the saved data:
\itemize{
\item 0 - means little-endian byte order, format used on PC/Intel machines
\item 1 - means big-endian (aka IEEE, aka "network") byte order, format
used on UNIX and Macintosh machines
}
}
}
Fields \code{samples}, \code{lines}, \code{bands}, \code{data type} are
required, while \code{header offset}, \code{interleave}, \code{byte order} are
optional. All of them are in form of integers except \code{interleave} which
is a string.
This generic format allows reading of many raw file formats, including those
with embedded header information. Also it is a handy binary format to
exchange data between PC and UNIX/Mac machines, as well as different
languages like: C, Fortran, Matlab, etc. Especially since header files are
simple enough to edit by hand.
File type supported by most of GIS (geographic information system) software
including: ENVI software, Freelook (free file viewer by ENVI), ArcGIS, etc.
}
\value{ Function \code{read.ENVI} returns either a matrix or 3D array.
Function \code{write.ENVI} does not return anything.}
\author{Jarek Tuszynski (SAIC) \email{jaroslaw.w.tuszynski@saic.com}}
\seealso{
Displaying of images can be done through functions: \code{\link[graphics]{image}},
\code{\link[fields]{image.plot}} and \code{\link[fields]{add.image}} from
\pkg{fields} or \code{\link[spatstat]{plot.im}} from \pkg{spatstat}.
ENVI files are practically C-style memory-dumps as performed by
\code{\link{readBin}} and \code{\link{writeBin}} functions plus separate
meta-data header file.
GIF file formats can also store 3D data (see \code{\link{read.gif}} and
\code{\link{write.gif}} functions).
Packages related to GIS data: \pkg{shapefiles}, \pkg{maptools}, \pkg{sp},
\pkg{spdep}, \pkg{adehabitat}, \pkg{GRASS}, \pkg{PBSmapping}.
}
\examples{
X = array(1:60, 3:5)
write.ENVI(X, "temp.nvi")
Y = read.ENVI("temp.nvi")
stopifnot(X == Y)
readLines("temp.nvi.hdr")
d = c(20,30,40)
X = array(runif(prod(d)), d)
write.ENVI(X, "temp.nvi", interleave="bil")
Y = read.ENVI("temp.nvi")
stopifnot(X == Y)
readLines("temp.nvi.hdr")
file.remove("temp.nvi")
file.remove("temp.nvi.hdr")
}
\keyword{file}
\concept{GIS data I/O}
|
