using mne.chpi tools {Disarmed}

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Hi there,
I'd like to play around with the head position information from some raw
fif files. I have been using the maxfilter program to extract the head
position files (the 6 quaternion variables) for some of the data, and I've
been importing that using chpi.read_head_pos() and that works fine. But I
also have some raw data that I'd like to use, but that is failing.
I can use the maxfilter gui to review the head positions, so I know the
data is there.
I am following the plot head positions tutorial
io.read_raw works fine, chpi.compute_chpi_amplitutdes works,
chpi.compute_chpi_locs seems to work, but then chpi.compute_head_pos I get
<ipython-input-88-83e389120352>:1: RuntimeWarning: t=598.850: 0/4
good HPI fits, cannot determine the transformation (0.16, 0.21, 0.18, 0.18)!
and the array in the output dictionary is empty.
I am running mne 21.0 (it works on the old CentOS6.7 without the 3d
plotting. I have it working on Ubuntu for 3d visualisations, finally, if
you remember my other thread from a while ago).

Here are the commands I'm using:
            raw = concat.concat_func(activeSubject, task, data_path,
defhead, mc)
            chpi_amplitudes = mne.chpi.compute_chpi_amplitudes(raw)
            chpi_locs = mne.chpi.compute_chpi_locs(,
            head_pos= mne.chpi.compute_head_pos(, chpi_locs,
Any suggestions? Would it be helpful if I shared a bit of data?
Thank you,

MEG Technician
The Mind Research Network
1101 Yale Blvd. NE
Albuquerque, New Mexico 87106
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