M4_Large_Whole.stl angular vector positions

kunheekunhee London
edited August 2018 in Headware
Hi,

I am using Cython + Daisy mark 4, using frame printed using M4_Large_Whole.stl.

I am in need of the exact angles at which the electrodes are pointing. 
Unfortunately, I don't have the exact dimensions of the frame, and cannot derive from it.

Could you please advise the angles or vectors of each electrodes?'
If not, could you please provide any geometric dimensions you do have?


Kind Regards,
Kunhee Lee

Comments

  • BillhBillh
    If an exact angle is what you need, note that the head shape and electrode projection depth will influence those angles, so if you need 1-degree precision, those angles will vary from subject to subject with the same frame in use.

    You might instead mark the head where the electrodes are placed when the frame is in use, and then measure the angles from the head, not the frame. If you have no frame to apply to a given head to get the measurements, you are not going to have precise (sub 1 degree) angles either.



  • kunheekunhee London
    hello Billh,

    thanks for the comment. 
    Whilst I completely agree that I cannot get precise angles of electrodes on the head by using angles of electrodes on frame, I actually just need the angles of electrodes on the frame. To be even more precise, I just need the angles normal to the slot on the frame. 

    Would you kindly be able to assist further regarding this matter?

    Kind Regards,
    Kunhee Lee
  • BillhBillh
    Since the electrodes are not in the same plane as the frame, I don't think I can help you in a way that is accurate. Sorry. You should use the angles of the International 10-20 system instead.

  • BillhBillh
    edited August 2018
    Biosemi has a lot of good documentation, including of the EEG spherical angles:



  • kunheekunhee London
    Thanks billh!
    this is fine for me!

    Thanks,
    Kunhee Lee
  • ThreeFormThreeForm NYC
    Hi. I just saw this so I'm ffollowing for those with similar questions. You can derive exact angles from the "Metadome" geometry provided in the M4 Dev kit here: https://github.com/OpenBCI/Ultracortex/tree/master/Mark_IV/DevKit

    The Metadome STL vertices define electrode locations, and the vertex normals define the electrode angles. The STL can be imported into CAD as a surface, and construction plane can be built to place your geometry. A simple way to place your own electrode geometry in a parametric way (so changes propagate) is to import your electrode assembly (as a mesh) into Blender to place copies at each vertex.

    To do that, select (right click) the Metadome, the shift+right click your electrode, then ctrl+P to parent, then in the Object tab click "Verts" in the Duplication section. Finally, shift+ctrl+A to "make duplicates real". This provides an oriented array of parts at each vertex.
  • ThreeFormThreeForm NYC
    I should also add that the placement can shifted ailing the vertex normals (in Blender) by editing the source object. If you switch to edit mode, select all vertices with "A", drag them downward with "G", then enter "-25" in the z-axis field in the Translate panel on the left, the original origin of the electrode assembly would now be moved to the scalp surface (assuming the Medium Metadome was imported for the Array).
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