Projection parameter??

[Cloud Hidden]

What's the viewDistance parameter in the Projection command do? I've figured out that small numbers make the objects smaller and large numbers make it bigger, while negative numbers turn it upside down. But I

can't figure out how it related to the SetViewVector parameters or the physical concept of a

camera. If I use 100' as a value, that's 100' from where and to where?

[Andrew Bell@NV]

quote:

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Originally posted by Cloud Hidden:

What's the viewDistance parameter in the Projection command do? I've figured out that small numbers make the objects smaller and large numbers make it bigger, while negative numbers turn it upside down. But I

can't figure out how it related to the SetViewVector parameters or the physical concept of a

camera. If I use 100' as a value, that's 100' from where and to where?

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You may want to try to understand the concept of a view frustum; see http://oss.ckk.chalmers.se/dictionary/php/record.php?Id=282 for a visual. The various viewing parameters are defining that frustum. I believe the view distance is the distance to the near plane, or near clipping plane. The larger it is, the farther away that plane is, and the narrower your field of view is.

If you prefer to think of a camera, it would be like the focal distance (or focal length) of the lens. With a telephoto lens, the more you zoom, the longer the focal distance, and the larger the objects appear.

[Cloud Hidden]

OK, I grok that (and thanks for pointing to a definition that referenced a hither plane and yon plane...that tickled my funny bone!). But I'm still at a loss for the meaning of the specific number, and why it's a distance. What does 100' mean or what does 3' mean in this context, or are the specific values more arbitrary than I'm trying to make them be? With a camera, focal length is mm of lens to film, so I'm trying to make the specific viewdistance value make sense in that context. And speaking of which, that's how I look at the Perspective values, but they don't really correlate to typical wide angle/telephoto values, so I never quite know how to pick a value other than trial and error.

Thanks Andrew.