Bug in vector source estimate plotting

Describe the bug

This was reported to me by @rythorpe. The vector source estimate does not plot arrows for the somato data.

Steps and/or code to reproduce

Here is a gist to reproduce the problem. I don’t see any issue with the script. Indeed, if you do:

print(stc)

you get:

<VectorSourceEstimate  |  8155 vertices, subject : 01, tmin : -199.79521315838787 (ms), tmax : 199.79521315838792 (ms), tstep : 3.3299202193064645 (ms), data shape : (8155, 3, 121)>

and if you do:

print(stc.data.shape)

you get:

(8155, 3, 121)

indicating that the stc is vector.

Expected results

There should be an arrow plot

Actual results

but the plot shows:

Additional information

I’m on the latest master, commit 42948689e.

and mne.sys_info() gives:

Platform:      Linux-3.10.0-957.1.3.el7.x86_64-x86_64-with-centos-7.6.1810-Core
Python:        3.6.7 | packaged by conda-forge | (default, Feb 28 2019, 09:07:38)  [GCC 7.3.0]
Executable:    /autofs/space/meghnn_001/users/mjas/anaconda3/envs/mne/bin/python
CPU:           x86_64: 64 cores
Memory:        125.3 GB

mne:           0.20.dev0
numpy:         1.15.4 {blas=mkl_rt, lapack=mkl_rt}
scipy:         1.2.1
matplotlib:    3.0.2 {backend=Qt5Agg}

sklearn:       0.20.2
numba:         Not found
nibabel:       2.3.3
cupy:          Not found
pandas:        0.24.1
dipy:          0.15.0
mayavi:        4.7.0.dev0 {qt_api=pyqt5, PyQt5=5.9.2}
pyvista:       Not found
vtk:           8.1.2

[larsoner]

@GuillaumeFavelier feel free to try out the 3D version to see if you can get something satisfying. We can have an option for glyph='arrow2d' | 'arrow3d' or so if it ends up looking good

[drammock]

I haven’t looked at how this is currently handled in the code, so maybe this is a dumb idea, but it seems to me that you will never want your longest arrow to be longer than, say, 1/5 the width of a cerebral hemisphere at most. Would it be enough to always scale such that the longest arrow ends up that size?

On November 5, 2019 8:24:08 AM PST, Mainak Jas [e-mail] wrote:

Yes, the scale_factor does seem to improve things. Although it is still a bit hard to see the arrows depending on how you rotate the brain. Not sure if that’s expected. If the automatic logic is not so reliable, maybe one option is to add it as an option to tweak in the time_viewer ?