I am trying to load a Nexus event file (simulated data from ESS, so I’m a bit on my own here) and I am getting an error that is not terribly helpful:
Error in execution of algorithm LoadEventNexus:
NXopengroup(dae, IXdae) failed
Error in execution of algorithm Load:
NXopengroup(dae, IXdae) failed
I also get a warning which may or may not be related:
Empty proton_charge sample log. You will not be able to filter by time.
In firstLastPulseTimes: no ISO8601 offset attribute provided for event_time_zero, using UNIX epoch instead
(this is simulated data so there’s no offset.) Any idea what this could be? Setting log messages to debug gave me no more information. I’m using Mantid 6.11.0 on Mac.
Okay, I figured it out, but guys, this is not good.
In my nexus file, i have event data as a hardlink in the top level as '/entry/detector_{i}_events' where i is the panel number. This should be innocuous enough a name, right? Turns out, 'entry/detector_{i}_events' is hardcoded into LoadEventNexus to load as an ISIS-only Nexus file. So if it detects that datagroup, it tries to load it as an ISIS nexus file, and fails, because- shock- it’s NOT an ISIS nexus file.
The error happens here. This is from the adjustTimeOfFlightISISLegacy function. That’s odd, my file is not from ISIS. Well, it says in the docstring for this function:
So, the check for LoadEventNexus is in part checking for entry/detector_{i}_events, and decides it’s from ISIS if it finds it. That’s a bit too generic for a name for a facility check. What’s particularly infuriating is how long it took me to figure out; I had to dive into the source code to figure this out. The decision-making flow should at least show up in the debugging, I feel.
Anyway, I changed the name of these groups and now my file loads without issue. Hooray, I guess.
Dear Aaron,
Thank you for not only reporting the problem with LoadEventNexus, but also providing such a detailed description of the actual issue. I have created a GitHub issue for us to look at (LoadEventNexus error for Nexus files from outside ISIS · Issue #40490 · mantidproject/mantid · GitHub) to get it hopefully fixed for the next release.
All the best,
Silke
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