read.ENVI: Import of ENVI data as hyperSpec object

In hyperSpec: Work with Hyperspectral Data, i.e. Spectra + Meta Information (Spatial, Time, Concentration, ...)

Import of ENVI data as hyperSpec object

Description

This function allows ENVI data import as hyperSpec object.

read.ENVI.Nicolet should be a good starting point for writing custom wrappers for read.ENVI that take into account your manufacturer's special entries in the header file.

Usage

read.ENVI(
  file = stop("read.ENVI: file name needed"),
  headerfile = NULL,
  header = list(),
  keys.hdr2data = FALSE,
  x = 0:1,
  y = x,
  wavelength = NULL,
  label = list(),
  block.lines.skip = 0,
  block.lines.size = NULL,
  ...,
  pull.header.lines = TRUE
)

read.ENVI.HySpex(
  file = stop("read.ENVI.HySpex: file name needed"),
  headerfile = NULL,
  header = list(),
  keys.hdr2data = NULL,
  ...
)

read.ENVI.Nicolet(
  file = stop("read.ENVI: file name needed"),
  headerfile = NULL,
  header = list(),
  ...,
  x = NA,
  y = NA,
  nicolet.correction = FALSE
)

Arguments

file	complete name of the binary file
headerfile	name of the ASCII header file. If NULL, the name of the header file is guessed by looking for a second file with the same basename as file but hdr or HDR suffix.
header	list with header information, see details. Overwrites information extracted from the header file.
keys.hdr2data	determines which fields of the header file should be put into the extra data. Defaults to none. To specify certain entries, give character vectors containing the lowercase names of the header file entries.
x, y	vectors of form c(offset, step size) for the position vectors, see details.
wavelength, label	lists that overwrite the respective information from the ENVI header file. These data is then handed to initialize
block.lines.skip, block.lines.size	BIL and BIP ENVI files may be read in blocks of lines: skip the first block.lines.skip lines, then read a block of block.lines.size lines. If block.lines.NULL, the whole file is read. Blocks are silently truncated at the end of the file (more precisely: to header$lines).
...	currently unused by read.ENVI, read.ENVI.Nicolet hands those arguements over to read.ENVI
pull.header.lines	(internal) flag whether multi-line header entries grouped by curly braces should be pulled into one line each.
nicolet.correction	see details

Details

ENVI data usually consists of two files, an ASCII header and a binary data file. The header contains all information necessary for correctly reading the binary file.

I experienced missing header files (or rather: header files without any contents) produced by Bruker Opus' ENVI export.

In this case the necessary information can be given as a list in parameter header instead:

header$	values	meaning
samples	integer	no of columns / spectra in x direction
lines	integer	no of lines / spectra in y direction
bands	integer	no of wavelengths / data points per spectrum
`data type`		format of the binary file
	1	1 byte unsigned integer
	2	2 byte signed integer
	3	4 byte signed integer
	4	4 byte float
	5	8 byte double
	9	16 (2 x 8) byte complex double
	12	2 byte unsigned integer
`header offset`	integer	number of bytes to skip before binary data starts
interleave		directions of the data cube
	"BSQ"	band sequential (indexing: [sample, line, band])
	"BIL"	band interleave by line (indexing: [sample, line, band])
	"BIP"	band interleave by pixel (indexing: [band, line, sample])
`byte order`	0 or "little"	little endian
	1 or "big"	big endian
	"swap"	swap byte order

Some more information that is not provided by the ENVI files may be given:

Wavelength axis and axis labels in the respective parameters. For more information, see initialize.

The spatial information is by default a sequence from 0 to header$samples - 1 and header$lines - 1, respectively. x and y give offset of the first spectrum and step size.

Thus, the object's $x colum is: (0 : header$samples - 1) * x [2] + x [1]. The $y colum is calculated analogously.

Nicolet uses some more keywords in their header file. They are interpreted as follows:

description	giving the position of the first spectrum
z plot titles	wavelength and intensity axis units, comma separated
pixel size	interpreted as x and y step size (specify x = NA and y = NA)

These parameters can be overwritten by giving a list with the respective elements in parameter header.

The values in header line description seem to be microns while the pixel size seems to be in microns. If nicolet.correction is true, the pixel size values (i.e. the step sizes) are multiplied by 1000.

Value

a hyperSpec object

Functions

• read.ENVI.HySpex:

• read.ENVI.Nicolet:

Author(s)

C. Beleites, testing for the Nicolet files C. Dicko

References

This function was adapted from caTools::read.ENVI():

Jarek Tuszynski (2008). caTools: Tools: moving window statistics, GIF, Base64, ROC AUC, etc.. R package version 1.9.

See Also

caTools::read.ENVI()

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hyperSpec documentation built on May 29, 2024, 7:28 a.m.