mne-tools/mne-python — pull request #1205 by christianmbrodbeck (2014-03-27 19:08:06+00:00)
Title: WIP scale_source_space():  add support for vol source spaces

Trying to adapt scale_source_space to handle volume source spaces. As far as I can tell the additional source space entries that need scaling are:

* vox_mri_t
* src_mri_t
* interpolator

When looking at the transforms in my volume source space I created for fsaverage I was somewhat confused:

```py
>>> pprint(vsrc['src_mri_t'])
{'from': 2001,
'to': 5,
'trans': array([[ 0.01, 0. , 0. , -0.08],
[ 0. , 0.01, 0. , -0.12],
[ 0. , 0. , 0.01, -0.08],
[ 0. , 0. , 0. , 1. ]])}
>>> pprint(vsrc['vox_mri_t'])
{'from': 2001,
'to': 5,
'trans': array([[-0.001 , 0. , 0. , 0.12800001],
[ 0. , 0. , 0.001 , -0.12800001],
[ 0. , -0.001 , 0. , 0.12800001],
[ 0. , 0. , 0. , 1. ]])}
```

Shouldn't one be the inverse of the other? I.e.

```py
>>> sp.linalg.inv(vsrc['src_mri_t']['trans'])
array([[ 100.00000224, 0. , -0. , 8. ],
[ 0. , 100.00000224, -0. , 12. ],
[ 0. , 0. , 100.00000224, 8. ],
[ 0. , 0. , 0. , 1. ]])
```
Since source space coordinates seem to be in [m] I assume the MRI is in [mm]?

The `setup_volume_source_space()` documentation was not clear to me as to which MRI should be provided. I just used `orig.mgz`, is that maybe the problem? (@mluessi?)