Thanks! I actually realized that I can create the external loads also with px,py,pz defined as OriginOfForcePlate instead of CoP, therefore (using osimC3D(c3dpath,0) instead of osimC3D(c3dpath,1)) I no longer have the NaNs issue...

Thanks for your reply.
I was hoping for a 'column based' method rather than adding row by row, but it will do.

Hi all, I'm working with the API (OpenSim 4.4) in Matlab and when I read my c3d with osimC3D(c3dpath,1) I get NaNs in the CoP, therefore forceTable = c3d.getTable_forces() has NaNs that get written to my mot when I use c3d.writeMOT. Is there a way to fix this? I couldn't find any answer in the forum...