Aaron Lauda has a nice description using the package XY-pic [here][1] ([Wayback Machine](https://web.archive.org/web/20140215045442/http://www.math.columbia.edu/~lauda/xy/)).  There are commands that generate pieces of knots (such as crossings in various orientations), although I prefer just using the \crv "curve" command to make splines.


  [1]: http://www.math.columbia.edu/~lauda/xy/