Re: Ortho Cameras

Gavin Bell (
Wed, 12 Oct 1994 12:21:02 -0700

On Oct 11, 4:40pm, Linas Vepstas wrote:
> Gavin Bell wrote a while ago:
> > Implementing user interface that can deal with
> > either orthographic or perspective scenes is the hard part.
> What's hard? What am I missing?

"Zoom" is a little tricky. For perspective cameras, zoom corresponds
to the field-of-view, which must be greater than 0 and less than 180
degrees. For orthographic cameras, zoom corresponds to changing the
width/height of the projection, which must be greater than zero and
less than infinity. Coming up with a UI that works for both finite (0
to 180) and infinite ranges is a little annoying.

If you implement stereo viewing, you need to do slightly different
things for ortho and perspective. Etc.

You're right, all of this isn't really that big a deal, and it seems
that enough people want orthographic cameras that the extra work is
worth it.

> -----------
> I suggest replacing the height-angle with a screen height & width.

What units are the screen height and width in? Pixels? (NOoooooo..)

World coordinates at the near clipping plane? Far clipping plane?
Focal distance?

Inventor's model seems to work pretty well...