Scaling External Asymptote File within the Current Document

Question

I have diagrams generated in Asymptote stored in external files. Is it possible to input the files into my current LaTeX document and to choose the scale factor within the current document?

The following naive approach does not work:

\documentclass{article}
\usepackage{asymptote}
\begin{document}

A unit sphere, 1/4 size:
\begin{asy}[width=0.25\textwidth]
\input{asyfile}
\end{asy} 

\end{document}

Contents of asyfile:

import solids;
draw(unitsphere,gray);

(I use these diagrams in different contexts, so I do not want to pick the scaling within the Asymptote file.)

Answer 1

It is tempting to use the TeX commands inside the asy environment, but it would result in a syntax error. Inside the Asymptote code TeX commands are allowed and useful only surrounded by string delimiters for example, in a label or texpreamble command, so don't use TeX \input command inside the asy environment, instead of \input{asyfile} use the Asymptote code include asyfile; to include the external .asy file.

For example:

\documentclass{article}
\usepackage{asymptote}
\begin{document}

A unit sphere, 1/4 size:
\begin{asy}[width=0.25\textwidth]
include asyfile; // but not `\input{asyfile}` 
\end{asy} 

\end{document}