I want to increase the \headheight in Beamer, Copenhagen.
I tried, \setlength{\headheight}{10in}, did not seem to work.
Edit:
My previous answer was actually valid with the Sidebar outer theme, it is not as simple with Split, which is used by Copenhagen. It explains the error you got, since \beamer@headheight is not defined in Split.
Answer:
You can use the following
\makeatletter
\newdimen\beamer@headheight
\beamer@headheight=10in
\setbeamertemplate{headline}{
\leavevmode%
\@tempdimb=2.4375ex%
\ifnum\beamer@subsectionmax<\beamer@sectionmax%
\multiply\@tempdimb by\beamer@sectionmax%
\else%
\multiply\@tempdimb by\beamer@subsectionmax%
\fi%
\ifnum\@tempdimb<\beamer@headheight
\setlength{\@tempdimb}{\beamer@headheight}
\fi
\ifdim\@tempdimb>0pt%
\advance\@tempdimb by 1.125ex%
\begin{beamercolorbox}[wd=.5\paperwidth,ht=\@tempdimb]{section in head/foot}%
\vbox to\@tempdimb{\vfil\insertsectionnavigation{.5\paperwidth}\vfil}%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.5\paperwidth,ht=\@tempdimb]{subsection in head/foot}%
\vbox to\@tempdimb{\vfil\insertsubsectionnavigation{.5\paperwidth}\vfil}%
\end{beamercolorbox}%
\fi%
}
\makeatother
You define a new length \beamer@headheight you can modify easily. This is a modification of the Split outer theme that will check if your new head height is larger than the one set by Beamer; if it is true, it will use this new length. If not, it won't change anything to avoid to mess up the headline. If you always want to force the headline to have the \beamer@headheight height, you can simply use
\makeatletter
\newdimen\beamer@headheight
\beamer@headheight=20pt
\setbeamertemplate{headline}{
\leavevmode%
\begin{beamercolorbox}[wd=.5\paperwidth,ht=\beamer@headheight]{section in head/foot}%
\vbox to\@tempdimb{\vfil\insertsectionnavigation{.5\paperwidth}\vfil}%
\end{beamercolorbox}%
\begin{beamercolorbox}[wd=.5\paperwidth,ht=\beamer@headheight]{subsection in head/foot}%
\vbox to\@tempdimb{\vfil\insertsubsectionnavigation{.5\paperwidth}\vfil}%
\end{beamercolorbox}%
}
\makeatother
Undefined control sequence. <argument> \beamer@height \setlength{\beamer@headheight}{10pt}