[Ifeffit] Athena error reading file

[Bruce Ravel]

On Wednesday 26 August 2009 01:33:16 pm Christopher Allen wrote:
> Hi everyone,
>
> I have two scans taken at x19a of the NSLS (attached) recently that
> won't open in Athena.  Scans before and after these two had no problem,
> but these give the error reading file message.  This was true using
> whatever version of Athena is on their beamline computer and also
> version 0.8.056.

Chris,

Shelly and Carlo both gave good advice.  I'll offer a bit more, this
more specific to the situation of collecting data at NSLS.

Most (but not all) of the XAS beamlines at NSLS use the XDAC program
for data collection.  XDAC allows you to enter a few lines of comments
describing a scan or set of scans.  These comment lines are written to
the data file just above the line of dashes.

Athena uses Ifeffit to import data from column data files.  Ifeffit
uses some heuristics to try to figure out what part of the file is the
header and what part is the columns of data.  Matt did a fairly
amazing job -- Ifeffit gets that question right surprisingly often.
However, one situation that will always fool Ifeffit is when a line
among the headers looks like data.  In the context of Ifeffit,
"looking like data" means a line that has only numbers with no
non-numeric characters.

The upshot of this is that giving XDAC a comment like "3.71", while
probably meaningful to you, is guaranteed to make Ifeffit (and Athena)
unhappy.  Because XDAC writes out its headers without any
beginning-of-line character, instead relying on the line of dashes to
mark the boundary between header and data, an XDAC comment consisting
only of numeric characters will always trigger this problem.

Fortunately, the solution is trivial: be more verbose in the XDAC
comment box.

HTH,
B



-- 

 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/