Dear Felix, In general, the exact coordinate system+units in which the geometric positions of the data objects are defined is irrelevant, as long as they are the same across the different pieces of information that are combined to compute the leadfields. In other words, as long as the sensor positions, volume conduction model, and source model dipole positions share the same coordinate system and units, the result will be physically correct (yet the physical units of the leadfield may vary, which will be due to units, rather than to the coordinate system).
Indeed, if you want to compute the leadfields, you should use the anatomy data that is provided to you by us, which, as I mentioned previously, has been coregistered to the MEG sensors for you. As you can see, when you load one of the variables, e.g. the headmodel, the matlab data structure contains a field ‘coordsys’, and ‘unit’. These specify the coordinate system and metric units of the coordinates, respectively. You will see that the coordsys = ‘bti’; If I recall correctly, the units are in ‘mm’. If you need to convert this, you can use the ft_convert_units function in FieldTrip. Best wishes, Jan-Mathijs J.M.Schoffelen, MD PhD Senior Researcher, VIDI-fellow - PI, language in interaction Telephone: +31-24-3614793 Physical location: room 00.028 Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands > On 10 Jan 2018, at 05:38, Felix Yuan > <[email protected] > <mailto:[email protected]>> wrote: > > Dear HCP experts, > > Sorry to bother you, I am going to computing the leadfield of resting state > MEG preprocessed data. > > But in the fieldtrip pipeline, I need to give the coordsys as a parameter. > Can I use the anatomy data and MEG resting state data in the preprocessed > folder I downloaded from HCP? > Do I also need to transform the coordinate space of anatomy data to MEG data > space? Could you tell me Whether they have been co-registrated to the same > space or not? > > In this > website,http://www.fieldtriptoolbox.org/faq/how_are_the_different_head_and_mri_coordinate_systems_defined > > <http://www.fieldtriptoolbox.org/faq/how_are_the_different_head_and_mri_coordinate_systems_defined> > I found that if the anatomy data is in the CTF MRI (ALS) space, and MEG data > is in the 4D/BTi space (ALS), the units of them are different, with mm and m, > respectively. > > > Thank you for your attention. > Best wishes, > Felix > _______________________________________________ > HCP-Users mailing list > [email protected] <mailto:[email protected]> > http://lists.humanconnectome.org/mailman/listinfo/hcp-users > <http://lists.humanconnectome.org/mailman/listinfo/hcp-users> _______________________________________________ HCP-Users mailing list [email protected] http://lists.humanconnectome.org/mailman/listinfo/hcp-users
