[Radiance-general] help with view direction vector

[Thomas Bleicher]

On Sat, Feb 21, 2004 at 06:36:21PM -0800, Tyler Riddle wrote:
> Hello,
> 
> I have just started playing with Radiance and I can't

Wellcome!

> figure out how to use the view direction vector. I
> have previous experience using Pov-Ray but I just
> can't find documentation that describes exactly what
> the view vector is or what the values mean. Can anyone

First information for Pov-Ray users:

    You made it through the mirror!

Radiance is based on a right-handed coordinate system.

For elevations this means:

X points right
Y points into the screen and
Z points up

For plan views:

X points right
Y points up
Z points out of the screen


About the view vector:

You define views basically by giving the position of the
observer (viewpoint, -vp) in world coordinates and the
direction (not the point!) of his view (view direction, -vd).
For views, there is only the global coordinate system, so
the direction is given in dx, dy and dz of the global system.

If we picture a scene with a room centered at (0,0) and an
observer looking from east (10,0) into the room, his view
vector is (-1,0). Another observer at (10,-3) has a vector
of (-1,0.3). The view vector will be unified internally but
to define it in "rview"/"rvu" you can enter any value you like.

> here either point me towards documentation that
> describes it or give me that crictical piece of
> knowledge that makes it obvious to someonme who knows
> alot of math?

No PhD needed to use it!

I'm a bit out of touch and can't point you to URLs but
the Radiance home page and www.radiance-online.org will
have sections about documentation.
Search for the introduction of Ward/Shakespears book
"Rendering with Radiance". The intro chapter is/was
available as pdf and contains a simple tutorial. You may
have to replace every occurence of "rview" with "rvu" 
since the application was renamed recently. It depends
on where and when you got your Radiance distribution.

> Thanks for your time,
> Tyler Riddle

Beautiful pictures,

Thomas