.roh file format: Ruby parsing library

Avantes USB spectrometers are supplied with a Windows binary which generates one ROH and one RCM file when the user clicks "Save experiment". In the version of 6.0, the ROH file contains a header of 22 four-byte floats, then the spectrum as a float array and a footer of 3 floats. The first and last pixel numbers are specified in the header and determine the (length+1) of the spectral data. In the tested files, the length is (2032-211-1)=1820 pixels, but Kaitai determines this automatically anyway.

The wavelength calibration is stored as a polynomial with coefficients of 'wlintercept', 'wlx1', ... 'wlx4', the argument of which is the (pixel number + 1), as found out by comparing with the original Avantes converted data files. There is no intensity calibration saved, but it is recommended to do it in your program - the CCD in the spectrometer is so uneven that one should prepare exact pixel-to-pixel calibration curves to get reasonable spectral results.

The rest of the header floats is not known to the author. Note that the newer version of Avantes software has a different format, see also https://kr.mathworks.com/examples/matlab/community/20341-reading-spectra-from-avantes-binary-files-demonstration

The RCM file contains the user-specified comment, so it may be useful for automatic conversion of data. You may wish to divide the spectra by the integration time before comparing them.

Written and tested by Filip Dominec, 2017-2018

File extension

roh

KS implementation details

License: CC0-1.0

This page hosts a formal specification of .roh file format using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Parse a local file and get structure in memory:

data = AvantesRoh60.from_file("path/to/local/file.roh")

Or parse structure from a string of bytes:

bytes = "\x00\x01\x02..."
data = AvantesRoh60.new(Kaitai::Struct::Stream.new(bytes))

After that, one can get various attributes from the structure by invoking getter methods like:

data.unknown1 # => get unknown1

Ruby source code to parse .roh file format

avantes_roh60.rb

# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

require 'kaitai/struct/struct'

unless Gem::Version.new(Kaitai::Struct::VERSION) >= Gem::Version.new('0.7')
  raise "Incompatible Kaitai Struct Ruby API: 0.7 or later is required, but you have #{Kaitai::Struct::VERSION}"
end


##
# Avantes USB spectrometers are supplied with a Windows binary which 
# generates one ROH and one RCM file when the user clicks "Save
# experiment". In the version of 6.0, the ROH file contains a header 
# of 22 four-byte floats, then the spectrum as a float array and a 
# footer of 3 floats. The first and last pixel numbers are specified in the 
# header and determine the (length+1) of the spectral data. In the tested 
# files, the length is (2032-211-1)=1820 pixels, but Kaitai determines this 
# automatically anyway.
# 
# The wavelength calibration is stored as a polynomial with coefficients
# of 'wlintercept', 'wlx1', ... 'wlx4', the argument of which is the
# (pixel number + 1), as found out by comparing with the original 
# Avantes converted data files. There is no intensity calibration saved,
# but it is recommended to do it in your program - the CCD in the spectrometer 
# is so uneven that one should prepare exact pixel-to-pixel calibration curves 
# to get reasonable spectral results.
# 
# The rest of the header floats is not known to the author. Note that the 
# newer version of Avantes software has a different format, see also
# https://kr.mathworks.com/examples/matlab/community/20341-reading-spectra-from-avantes-binary-files-demonstration
# 
# The RCM file contains the user-specified comment, so it may be useful
# for automatic conversion of data. You may wish to divide the spectra by 
# the integration time before comparing them.
# 
# Written and tested by Filip Dominec, 2017-2018
class AvantesRoh60 < Kaitai::Struct::Struct
  def initialize(_io, _parent = nil, _root = self)
    super(_io, _parent, _root)
    _read
  end

  def _read
    @unknown1 = @_io.read_f4le
    @wlintercept = @_io.read_f4le
    @wlx1 = @_io.read_f4le
    @wlx2 = @_io.read_f4le
    @wlx3 = @_io.read_f4le
    @wlx4 = @_io.read_f4le
    @unknown2 = Array.new(9)
    (9).times { |i|
      @unknown2[i] = @_io.read_f4le
    }
    @ipixfirst = @_io.read_f4le
    @ipixlast = @_io.read_f4le
    @unknown3 = Array.new(4)
    (4).times { |i|
      @unknown3[i] = @_io.read_f4le
    }
    @spectrum = Array.new((((ipixlast).to_i - (ipixfirst).to_i) - 1))
    ((((ipixlast).to_i - (ipixfirst).to_i) - 1)).times { |i|
      @spectrum[i] = @_io.read_f4le
    }
    @integration_ms = @_io.read_f4le
    @averaging = @_io.read_f4le
    @pixel_smoothing = @_io.read_f4le
    self
  end
  attr_reader :unknown1
  attr_reader :wlintercept
  attr_reader :wlx1
  attr_reader :wlx2
  attr_reader :wlx3
  attr_reader :wlx4
  attr_reader :unknown2
  attr_reader :ipixfirst
  attr_reader :ipixlast
  attr_reader :unknown3
  attr_reader :spectrum
  attr_reader :integration_ms
  attr_reader :averaging
  attr_reader :pixel_smoothing
end