[help-3dldf] Re: button-hole problem

[Laurence Finston]

> Minor disagreement about coordinatization 
> for eye or camera or screen display:
> 
> My choice of the film plane F as R x R x {m}, and the projection
> center always at the origin (0,0,0) seems more convenient since
> zooming is *less awkward* than when you choose the center at
> (0,0,-m).

In "my" method (actually, it's from one of the books I've used, probably Huw
Jones, _Computer Graphics Through Key Mathematics_, or perhaps from a book by
Stephen Harrington, whose title I've forgotten), 
the plane of projection is transformed to the x-y plane, so I can just write
the x and y values of the "projective coordinates" (as I call them) to the
MetaPost output.

> 
> Recall that m > 0 is my zoom factor.

This is true of "my" method as well.  

I'm not arguing with you.  I have no particular emotional attachment to the
method I use.  If it turns out to be advantageous to change it, I'd be quite
happy to do so.  I don't think it would be too difficult.  If not, I might as
well leave it as it is.

> PS.  When you quote from another list please
> identify the speaker and date.

Okay.

Thanks.

Laurence