Hi, I was hoping to use the CSD toolbox (Matlab) on some of my 128 channel Biosemi data however I am unable to get the correct montage to allow this as the toolbox is designed for the 10-20 system. For the CSD toolbox the spherical coordinates for locations where the three great circles of the x-y, x-z, and y-z planes intersect are straightforward (e.g., for Oz: theta = -90, phi = 0; for Cz: theta = 0, phi = +90; for T8: theta = 0, phi = 0). Intermediate locations on these great circles are quarter (22.5°) or quintile (18.0°) sections of the respective rectangular arcs (e.g., for O1, theta is -90 - 1*18 = -108, phi = 0; for Pz, theta = -90, phi is 2 * 22.5 = +45; for P8, theta is 2 * -18 = -36, phi = 0). Similarly, locations on the small circle combining nasion and inion are a quarter rectangular arc downwards (e.g., for P10, theta is 2 * -18 = -36, phi = -22.5).

Can anyone provide a formulate for converting the spherical coordinates provided on the Biosemi website into this format?