# coordinate frames

**URL:** <https://mne.discourse.group/t/coordinate-frames/141>\
**Category:** Mailing List Archive (read-only)\
**Tags:** list-archive\
**Created:** [July 7, 2009, 5:55pm UTC](https://mne.discourse.group/t/coordinate-frames/141 "2009-07-07T17:55:17Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\
**Post date:** [July 7, 2009, 5:55pm UTC](https://mne.discourse.group/t/coordinate-frames/141/1 "2009-07-07T17:55:17Z")

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Hello,

I have a few questions about the coordinate systems MNE uses.

1) When I use the Matlab toolbox functions mne\_read\_bem\_surfaces,  
fiff\_read\_mri, and mne\_read\_surfaces, the resulting structures are all  
in the same coordinate system? If so, the transformation matrix in  
result.trans.trans is all that needs to be used to take these  
structures to the head coordinate system? If not, how can I take these  
structures from the MRI coordinates to head coordinates? (I'm assuming  
that the matlab functions to read the MEG data already return the data  
in the head frame, but let me know if I'm wrong about that too).

2) mne\_analyze has a great tool to align the MEG data to MRIs using  
the digitized points. I figure that the transformation matrix after  
the aligning process is stored in the COR\* files in the subject's  
folder. In this case, if I open that COR\*.fif file in matlab with  
fiff\_read\_mri, can I just use the trans.trans matrix that comes with  
it to take the MRI to the head coordinate system?

3) When I use mne\_read\_surfaces I get an array with two surfaces, one  
for each hemisphere. Is there a quick way to plot them together as one  
connected brain (e.g. as it is done in mne\_analyze visualizer)? If I  
just plot both arrays they get plotted on top of each other...

Thanks,

Gus