to be used by `trplot()` etc. Options for: - simple line segment - arrow, eg. quiver - arrow with 3D open head, eg. [quiver5](https://www.mathworks.com/matlabcentral/fileexchange/22351-quiver-5) - arrow with 3D cone head, eg. [arrow3](https://www.mathworks.com/matlabcentral/fileexchange/14056-arrow3) - full 3D, cylinder as shaft, cone as head, eg. [3D Arrow](https://www.mathworks.com/matlabcentral/fileexchange/12274-3d-arrow-with-many-color-parameter-options)
