# help with view direction vector

Hello,

I have just started playing with Radiance and I can't
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
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?

Tyler Riddle

···

=====
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aim: TheMastaSpice

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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

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
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

Tyler Riddle

Beautiful pictures,

Thomas

···

On Sat, Feb 21, 2004 at 06:36:21PM -0800, Tyler Riddle wrote:

Hi,

the view vector is or what the values mean. Can anyone
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?

The view vector is just the difference between the point of
interest and the position of your camera. If you want to look at
the point (0,0,0) with the camera at (-1,2,-5) the view vector
is (1,-2,5). Don't forget the up-vecor, (0,1,0) or (0,0,1) should
be fine for the most cases (according to the orientation of your
scene, Radiance uses rather (0,0,1) (gensky creates a z-upward
oriented sky), but if are more familiar with 3d-programs with y
for up, it might be easier to build scenes that way with (0,1,0).

Sabine