[Rd] Correct NAMESPACE approach when writing an S3 method for a generic in another package

[Gavin Simpson]

Dear List,

In one of my packages I have an S3 method for the plot3d generic
function from package rgl. I am trying to streamline my Depends
entries but don't know how to have

plot3d(foo)

in the examples section for the plot3d method in my package, without
rgl being in Depends.

Note that I importFrom(rgl, plotd3d) and register my S3 method via
S3Method() in the NAMESPACE.

If rgl is not in Depends but in Imports, I see this when checking the package

> ## 3D plot of data with curve superimposed
> plot3d(aber.pc, abernethy2)
Error: could not find function "plot3d"

I presume this is because rgl's namespace is only loaded but the
package is not attached to the search path.

Writing R extensions indicates that one can export from a namespace
something that was imported from another package namespace. I thought
that might help the situation, and now the code doesn't raise an
error, I get

* checking for missing documentation entries ... WARNING
Undocumented code objects:
  ‘plot3d’
All user-level objects in a package should have documentation entries.
See the chapter ‘Writing R documentation files’ in the ‘Writing R
Extensions’ manual.

as I don't document plot3d() itself.

What is the recommended combination of Depends and Imports plus
NAMESPACE directives etc that one should use in this situation? Or am
I missing something else?

I have a similar issue with my package including an S3 method for a
generic in the lattice package, so if possible I could get rid of both
of these from Depends if I can solve the above issue.

Thanks in advance.

Gavin

-- 
Gavin Simpson