FT_APPENDSENS concatenates multiple sensor definitions that have been processed
separately.
Use as
combined = ft_appendsens(cfg, sens1, sens2, ...)
A call to FT_APPENDSENS results in the label, pos and ori fields to be
concatenated, and the tra matrix to be merged. Any duplicate electrodes
will be removed. The labelold and chanposold fields are kept under the
condition that they are identical across the inputs.
See also FT_ELECTRODEPLACEMENT, FT_ELECTRODEREALIGN, FT_DATAYPE_SENS,
FT_APPENDDATA, FT_APPENDTIMELOCK, FT_APPENDFREQ, FT_APPENDSOURCE