\pageref, but for columns

Question

I need to point to a label on a page, but as my text is layed out in two columns, I'd also like to include the column (1 or 2). Is there a way to find out which column a label is in?

\documentclass{icgg}
\begin{document}
\section{First chapter}
\label{explanation}
Some text explaining some things.
...
... see page \pageref{explanation} for ...

\end{document}    

I'd like to use something like:

see page \pageref{explanation}, column \columnref{explanation} for ...

Possible?

ps. the document class is provided by someone else and it defines the two-column format.

Answer 1

This is an attempt.

The class icgg.cls loads hyperref. We create a new command \collabel which is executed each time a \label command is issued.

If, for example, you issue \label{foo} a new label called col:foo is created at the same point of the document. if you want to know the column to which \label{foo} refers to, you have to use the command \columnref{col:foo}.

Here's an example (replace \documentclass[twocolumn]{article} \usepackage{hyperref} with \documentclass{icgg} in your document):

\documentclass[twocolumn]{article}
\usepackage{hyperref}
\usepackage{lipsum} %only for the example

\makeatletter
\AtBeginDocument{%
\let\oldlabel\label
\newcommand*\collabel[1]{%
  \begingroup
    \protected@write\@auxout{}{%
      \string\newlabel{col:#1}{%
        {\if@firstcolumn 1\else 2\fi}%
        {}%
        {}%
        {}%
        {}%
      }%
    }%
  \endgroup
}
\renewcommand*\label[1]{%
  \collabel{#1}\oldlabel{#1}
}
\def\columnref#1{%
  \HyRef@StarSetRef{#1}\@firstoffive
}
}
\makeatother

\begin{document}

\section{First section}\label{sec:first}
\lipsum[1-4]

\section{Second section}\label{sec:second}
\lipsum[1-3]\label{sec:third}

Section \ref{sec:first} starts at page \pageref{sec:first} in column \columnref{col:sec:first}, 
while section \ref{sec:second} starts at page \pageref{sec:second} in column \columnref{col:sec:second}

\end{document} 

Output:

Zoom on the relevant part:

Note that the command \if@firstcolumn sometimes fails to detect the right column, so you may have some wrong references.