I am a beginner in Brainstorm and trying to follow the resting state tutorial (https://neuroimage.usc.edu/brainstorm/Tutorials/HCP-MEG).
If you are a new Brainstorm user, I recommend you start by following the introduction tutorials first (all the section "Get started" on the tutorial page), using the example dataset provided. Only start reading advanced tutorials when you are familiar with the environment.
Our reference resting state MEG tutorial is the other one, based on the OMEGA database: https://neuroimage.usc.edu/brainstorm/Tutorials/RestingOmega
It does not have any missing information, and we update it more actively.
Here, it is said " 3D digitization using a Polhemus FASTRAK-III (head localization coils and head shape) " and tried to import the ".pos" file but could not find it in the folders.
There is no mention to this .pos file anywhere because it doesn't exist indeed. As explained in the tutorial, these points were removed for anonymization purposes by the research group that prepared the MEG-HCP dataset. We do not agree with this approach because we do not consider that these Polhemus points are not features that can help identifying the subjects. We complained about it but there is apparently nothing that can be done.
Even if these points were available, they would be embedded in the 4D MEG files, not available as a separate .pos file. Just stick to the instructions given by the tutorial, there is nothing that you are supposed to do that is not written in there. If you find any incoherence in the tutorials (which may happen, especially with tutorials we don't update frequently), please let us know.
Does this mean that I cannot have access the head points?
This is exactly what is written, indeed.
If it is impossible to coregister accurately, would not it cause problems in the later stages?
Yes, it causes problems. This is discussed in this tutorial, but more detailed in the introduction tutorials:
https://neuroimage.usc.edu/brainstorm/Tutorials/ChannelFile
I would be glad if someone can explain the idea behind of coregistration regarding HCP while using Brainstorm?
We can't do the coregistration in Brainstorm, we use the registration done in FieldTrip. See this paragraph in the tutorial:
The FieldTrip team computed this registration with their tools and distribute only the final transformation matrix (MEG/anatomy/*_MEG_anatomy_transform.txt). This matrix is imported automatically here and gives good results, but unfortunately we cannot reproduce or double-check the quality of the registration.