# BSDF orientation vector

Hi list, hi Greg,

I have a question concerning the BSDF "up-vector".
For e.g. a facade-mounted fenestration system the definition of the vector
is clear.
But what, if I have a BSDF defining the material properties and use this
BSDF to
simulate the BSDF of a daylighting system (i.e. curved specular lamellae)?

The comment in m_bsdf.c says that the "up-vector" together with the surface
normal
defines the local coordinate system. How exactly is that done??
Unfortunately I did
not have time yet to dig deeper into the BSDF-code to find that out...

Cheers,
David

The code is pretty simple. So long as the "up vector" is not parallel to the surface normal, it is used to orient the 0-degree azimuth position by projecting it into the plane of the surface normal at the ray intersection point. Make sense?

-Greg

ยทยทยท

From: David Geisler-Moroder <[email protected]>
Date: May 15, 2012 12:20:15 AM PDT

Hi list, hi Greg,

I have a question concerning the BSDF "up-vector".
For e.g. a facade-mounted fenestration system the definition of the vector is clear.
But what, if I have a BSDF defining the material properties and use this BSDF to
simulate the BSDF of a daylighting system (i.e. curved specular lamellae)?

The comment in m_bsdf.c says that the "up-vector" together with the surface normal
defines the local coordinate system. How exactly is that done?? Unfortunately I did
not have time yet to dig deeper into the BSDF-code to find that out...

Cheers,
David

1 Like

Ok, perfect -- this is exactly what I hoped it to be!

Thanks for the fast response,
cheers,
David

ยทยทยท

2012/5/15 Gregory J. Ward <[email protected]>

The code is pretty simple. So long as the "up vector" is not parallel to
the surface normal, it is used to orient the 0-degree azimuth position by
projecting it into the plane of the surface normal at the ray intersection
point. Make sense?

-Greg

> From: David Geisler-Moroder <[email protected]>
> Date: May 15, 2012 12:20:15 AM PDT
>
> Hi list, hi Greg,
>
> I have a question concerning the BSDF "up-vector".
> For e.g. a facade-mounted fenestration system the definition of the
vector is clear.
> But what, if I have a BSDF defining the material properties and use this
BSDF to
> simulate the BSDF of a daylighting system (i.e. curved specular
lamellae)?
>
> The comment in m_bsdf.c says that the "up-vector" together with the
surface normal
> defines the local coordinate system. How exactly is that done??
Unfortunately I did
> not have time yet to dig deeper into the BSDF-code to find that out...
>
> Cheers,
> David