PLink draws piecewise linear link projections. Components may be
points, PL arcs, or PL circles. Line segments are oriented consistently in
each component. Different components are different colors.
The window can be resized to allow for different sizes of link
projections, and the arrow keys can be used to slide the projection
around in order to make more room on one side or another. The keys
‘+’, ‘-‘, and ‘0’ can be used to zoom in, zoom out, or resize the
diagram to fit the size of the window.
The “Tools” menu can be used to make the projection alternating
(provided that all components are circles), or to clear the screen, or
to reflect the projection in the xy-plane, changing all crossings.
The “Preserve diagram” option disables any operation which could
change the combinatorics of the diagram; a vertex can be moved, but it
cannot be moved across an edge and its adjacent edges cannot be moved
across a vertex. The “Smooth” option opens a new window with a smooth
version of the diagram, rendered with cubic Bezier splines. When used
within SnapPy, the “Tools” menu includes the “Send to SnapPy” command.
There also are options in the “Tools” menu for zooming or panning
the diagram, but these operations are usually more easily done with
the arrow keys or the ‘+’, ‘-‘, and ‘0’ keys.
The “File” menu can be used to save the projection as a SnapPea
link projection file. (This can be done from the drawing state as
well, in which case the “hot vertex” is remembered in the file!). The
“File->Open File” command will read a SnapPea link projection file,
and restart drawing if the projection was saved while drawing.
The “Info” menu selects information about the link projection to be
displayed in the info line at the bottom. Various encoding schemes
for link projections are supported, as well as the blackboard framing
curves, expressed in meridian-longitude coordinates. Cutting and
pasting from the info line is supported. The numerical and
alphabetical Dowker-Thistlethwaite codes are displayed in an extended
form which includes a full description of the planar embedding. The
string printed in the info line is also accepted as input to SnapPy’s
Manifold constructor. Paste the DT code between the apostrophes in
Manifold(‘’). The “DT labels” option displays the indexing used in
computing the Dowker-Thistlethwaite codes.