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Date: Thu, 21 Sep 1995 22:51:08 -0400 (EDT)
From: Joe Angell <[e-mail]>
Subject: Re: Displacement Mapping (Newbie Question)
To: Jonathon Bowman <[e-mail]>
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>         I've done some computer animation, using 3D Studio (at school) and
> trueSpace (demo) but I'm considering purchasing Lightwave because of the
> price, and the extensive list of features.

Good call! :)

>         One topic that has been discussed a lot recently here on the mailing
> list is Displacement mapping.
>
>         I'm not completely sure exactly what displacement mapping (DM) is.
> >From what I've read, I understand that it allows you to deform an object
> using an image.
>
>         But how exactly does this work?  Does it actually deform the
> geometry of the object, or does is it just a visual effect, something that
> happens at render-time?

Displacement mapping is a process where the grey levels of an image are
used to determine the displacement (hence the name) of a point from it's
urrent position in an object.

Black is no displacement, White is 100% displacement (the displacement is
determined by the Texture Amplitude).  This displacement plysically moves
the points in the object (so any polygons with >3 sides'll probobly get
rendering errors, since they will likely become non-planar).  You can
also use Save Transformed to save the object in it's current state.

The "visual effect at render time" is known as Bump Mapping, which LW
also has, and has more limited uses, but a much lower polygon count (in
Diplacement Mapping, points are shifted, so if you have an image with any
setail, you need a lot of points, and thus a lot of polygons).  Bump
mapping is only an illusion of depth on the surface, while displacemnt
mapping actually IS depth in the surface.

>         For instance, could I use a displacement map of a human face on a
> sphere, and easily create a model of a human head, or would the actual
> geometry of the object remain a sphere, with a warping occuring to make it
> appear to be a face, or would this not work at all?

It would work, but I don't konw how well.  It may be better to just model
a real human face.  The trick is that the grey levels are used for the
height of the surface, so if you took a real persons face, where real
lighting was in effect, it would like pretty wierd, since once side of
his face would be brighter than another.

Come to think of it, I tried this once on a subdivided flat plane.  I got
a somewhat lopsided (since one half of his face was lit, it was more
raised than the other half) Han-Solo-In-Carbonite effect.  Kinda neat.

Some other uses are rippling fields of grass (using a Fractal Bumps
displacement of a field of grass), rippling waves that actually rise and
fall, faces rising off of walls, and many other effects that would only
be possible with large numbers of morph targets.  You can simulate smoke
and particle movements with some displacing, too, if you're tricky. :)

Hope this helps a bit...

-- Joe
--
Joe Angell <[e-mail]> sent this message.
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