How to change margins on odd/even pages

Question

I've tried this

\documentclass{article}

\usepackage{geometry}
\usepackage{changepage}
\usepackage{bophook}

\begin{document}

\AtBeginPage{%
\strictpagecheck
\ifnum\value{page}>1
    \ifoddpage
      \newgeometry{top=0.5cm, bottom=3cm}
    \else
      \newgeometry{top=3cm, bottom=0.5cm}
    \fi
\else
\fi
}

Test \newpage
Test 2 \newpage
Test 3
\end{document}

but it does not work.

The message error is

Improper \prevdepth. \newpage ...everypar {}\fi \par \ifdim \prevdepth

                                              >\z@ \vskip -\ifdim \prevd...

Is there a better way to do?

Why

I have a document in landscape "style" and I want the top margin to be 2cm on odd pages and 1cm on even pages, and the inverse for bottom margins.

Answer 1

A possible approach is to apply a different \voffset to each page. Here is one way to achieve that:

\documentclass{article}

\usepackage{bophook}

\begin{document}

\AtBeginPage{%
  \ifodd\count0 \global\voffset=0mm \else \global\voffset=25mm \fi
}

Test \newpage
Test 2 \newpage
Test 3
\end{document}

This moves the entire text block 25 mm down on even pages. Adjust your margins once and for all to achieve the effect you want.