Provide ktk.ext.n3d.read_n3d() to read Optotrak 3d acquisitions.
pip install git+https://github.com/felixchenier/kineticstoolkit_n3d
pip uninstall kineticstoolkit_n3d
import kineticstoolkit.lab as ktk
ts_markers = ktk.ext.n3d.read_n3d('filename.n3d')