# View-Up Vector

Hello everyone,

I've got a quick question regarding the "view up"-vector:
as far as I understand, the -vd vector in a view definition points
along the view direction (optical axis) of my virtual camera, whereas
the -vu points along the vertical (up) direction of my virtual camera.
So I guess they should be orthogonal. How does it affect
my view if I choose vu and vd such that they are not orthogonal
(Radiance only complains if vd and vu are exactly parallel) ?

Thanks,

Volker

Volker Hilsenstein wrote:

Hello everyone,

I've got a quick question regarding the "view up"-vector:
as far as I understand, the -vd vector in a view definition points
along the view direction (optical axis) of my virtual camera, whereas
the -vu points along the vertical (up) direction of my virtual camera.
So I guess they should be orthogonal. How does it affect
my view if I choose vu and vd such that they are not orthogonal
(Radiance only complains if vd and vu are exactly parallel) ?

That's really all that is necessary. In 3D space, you need two
non-parallel vectors to define a local carthesian coordinate
system (the third vector is deducted by the right hand rule).
If the two vectors given are not orthogonal, then Radiance will
internally recalculate the up-vector to the orthogonal direction,
which isn't very complicated to do. If you imagine the vertical
plane that includes both your view direction and the orthogonal
up direction (cutting the imaginative camera in a right and left
half), then the up vector that you give must lie within the upper
half of that plane, resp. the view will be arranged so that it
does.

-schorsch

···

--
Georg Mischler -- simulations developer -- schorsch at schorsch.com
+schorsch.com+ -- lighting design tools -- http://www.schorsch.com/

Volker Hilsenstein wrote:

Hello everyone,

I've got a quick question regarding the "view up"-vector:
as far as I understand, the -vd vector in a view definition points
along the view direction (optical axis) of my virtual camera, whereas
the -vu points along the vertical (up) direction of my virtual camera.
So I guess they should be orthogonal. How does it affect
my view if I choose vu and vd such that they are not orthogonal
(Radiance only complains if vd and vu are exactly parallel) ?

Howdy Volker,

vu and vd are always orthogonal per definition, unless of course you
make them parallel, which doesn't make sense. In all other cases vu will
be modified to lie within the projection plane, with vd being the
plane's normal.

See ya!

···

--
"Life is too short for core dumps"