Daniel Keefe, Robert Zeleznik, and David H. Laidlaw.
  <b>Tech-note: Dynamic Dragging for Input of 3D Trajectories</b>.
  In <i>IEEE Symposium on 3D User Interfaces</i>, 2008.
  <A HREF="http://vis.cs.brown.edu/docs/pdf/g/Keefe-2008-TDD.pdf.html">(pdf)</A>
  <A HREF="http://vis.cs.brown.edu/results/bibtex/Keefe-2008-TDD.bib">(bibtex:
  Keefe-2008-TDD)</A>.<br />