Block diagram
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://www.mathworks.com/matlabcentral/fileexchange/37103-avantes-to-matlab
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
This page hosts a formal specification of Avantes USB spectrometer ROH file 6.0 using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
meta:
id: avantes_roh60
title: Avantes USB spectrometer ROH file 6.0
file-extension: roh
xref:
wikidata: Q29960673
license: CC0-1.0
endian: le
doc: |
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://www.mathworks.com/matlabcentral/fileexchange/37103-avantes-to-matlab>
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
seq:
- id: unknown1
type: f4
- id: wlintercept
type: f4
- id: wlx1
type: f4
- id: wlx2
type: f4
- id: wlx3
type: f4
- id: wlx4
type: f4
- id: unknown2
type: f4
repeat: expr
repeat-expr: 9
- id: ipixfirst
type: f4
- id: ipixlast
type: f4
- id: unknown3
type: f4
repeat: expr
repeat-expr: 4
- id: spectrum
type: f4
repeat: expr
repeat-expr: ipixlast.to_i - ipixfirst.to_i - 1
- id: integration_ms
type: f4
- id: averaging
type: f4
- id: pixel_smoothing
type: f4