[Tex/LaTex] How to draw a monthly gantt chart with quarterly vgrid

Question

I recently updated my pgfgantt package, and can't figure out how to update one of my charts to draw properly under the new package. The chart has a two-tiered title, years over months. It also had a quarterly vertical grid. It's the quarterly vertical grid I'm having issues recreating.

My old working code was

\begin{tikzpicture}[x=.5cm, y=1cm]
  \begin{ganttchart}%
      [today=5.5, vgrid, vgrid lines list={4,7,...,\value{gtt@width}}]{19}
    \gantttitle{2012}{12} \gantttitle{2013}{7} \\
    \gantttitlelist{1,...,12}{1}\gantttitlelist{1,...,7}{1} \\
    \ganttgroup{Prospectus}{1}{7} \\
    %% more gantt items omitted
  \end{ganttchart}
\end{tikzpicture}

Following the examples in the package documentation I can create a dotted vertical grid for every other month, but not for every third month.

every other month:

\begin{tikzpicture}[x=.5cm, y=1cm]
  \begin{ganttchart}%
  [today=5.5, vgrid={draw=none, dotted}]{19}
    \gantttitle{2012}{12} \gantttitle{2013}{7} \\
    \gantttitlelist{1,...,12}{1}\gantttitlelist{1,...,7}{1} \\
    \ganttgroup{Prospectus}{1}{7} \\
  \end{ganttchart}
\end{tikzpicture}

but vgrid={draw=none, none, dotted} gives the error

ERROR: Package pgfkeys Error: I do not know the key '/tikz/none' and I am going to ignore it. Perhaps you misspelled it.

and vgrid={draw=*2{none}, dotted} gives the error

ERROR: Package xcolor Error: Undefined color `*2{none}'.

How can I get two skips followed by a dotted line?

Answer 1

The problem is with your syntax for the vgrid style list.

From PGF Gantt Documentation: A style list item has the general syntax *{<n>}{<style>}. You are correct in using the additional draw = none for no style on the vgrid but it should be contained within the style argument {<style>}.

So rather than vgrid={draw=*2{none}, dotted}

You should use vgrid={*2{draw=none}, dotted} This would produce the following output: