[Sigia-l] 3-D workflows

[Christopher Fahey [askrom]]

Ziya wrote:
> Do you consider QTVR 3D?

I don't consider it a 3-dimensional dataset. QTVR is just a 2d image
with fancy scroll mechanisms and fancy distortion algorithms meant to
imitate a 3D perspective, but the data is still a "bitmap" of pixels
with X and Y (no Z) coordinates (ignoring for now the color dimension).

> How about a globe that revolves on its own axis in front of 
> you while you stay stationary? 

If the globe has relief mountains sticking out of it, and/or if the user
can directly control the rotation along the X, Y, and Z axes, then yes.
If it's just a rotating video loop, then no. The question is this: Is
the globe a 2D map projected onto a sphere, or is it a 3D dataset like a
CAD model.

> Is the ability of the viewer to move physically and/or 
> virtually in a given
> space relative to a specific object the sole differentiator?

Yes, with a caveat: the user does not need to move their body, they
simply need to be able to move their *perspective* on the dataset.
Causing a 3D model of a tree to rotate is sematically the same as
walking around the tree. The differentiator, then, is the ability to
change perspective on the dataset.

2D images can be entirely grasped by just looking and not ever moving
the perspective. A QTVR image can convey the same information even if it
were just a still image of a panorama - if you think about it, the QTVR
technology actually inhibits the user's ability to view all the
information in the dataset! If one was able to (like the scene in blade
runner) look *behind* the objects depicted in a QTVR image, then it
might qualify as a 3D dataset. 

The viewer must be able to move and rotate their perspective in more
than 2 dimensions: X, Y, and Z. I'm not trying to set up some kind of
strict rule system about what is 3D and what is not - both of your
examples are clearly intended to blur the distinction between 2D and 3D
datasets, and hence to trip me up! I think we can agree that there is a
significant qualitative difference between an isometric projection of a
building that you can only look at and a scale model of a building that
you can stick your head into and peek around the corners.

-Cf

[christopher eli fahey]
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