# Daylight matrix - vu

Hello all,

I am trying to simulate light pipes with the
three phase method. Since the pipes are not straight I need to be sure that the
vectors I set are correct and I am a bit confused about what the “vu” vector
stands for. So here is what I did.

The room with the pipes is oriented towards
the northeast and the pipe bending is towards the southwest. I generated the BSDF through a model where the pipe
bending part is facing towards the –y axis. I attached a small picture to make it clearer. So here are some of my questions.

What should the "vu" be at the daylight matrix?
I am not sure which axis of the BSDF corresponds to the “vu”. My guess is that “vu” should be 1, 1, 0 or 1, -1, 0? Should the pipe
model from which I generate the BSDF be correctly oriented as well?

Is there any way to have the model of the
room oriented towards the north (y axis) and then set the correct orientation
via the “vu” or some other way?
Vayia

Hi Vayia,

Unfortunately genBSDF assumes that the two apertures of your system are
parrallel and rectangular, so i don't think your light pipe BSDF will be
valid. Greg has written a new tool, rfluxmtx, that will allow you to
generate a coefficient matrix for a relationship between arbitrary
polygons. Your model is a good example of what wasn't possible before that
is enabled by the new tools.

Unfortunately there's not much documentation of rfluxmtx other than the man
page. I'm working on providing a three-phase simulation example using
rfluxmtx hopefully ready by the workshop in September.

Best,
Andy

···

On Thu, Jul 31, 2014 at 4:53 AM, Vayia Koukouvayia <vaia13@msn.com> wrote:

Hello all,

I am trying to simulate light pipes with the three phase method. Since
the pipes are not straight I need to be sure that the vectors I set are
correct and I am a bit confused about what the "vu" vector stands for. So
here is what I did.

The room with the pipes is oriented towards the northeast and the pipe
bending is towards the southwest. I generated the BSDF through a model
where the pipe bending part is facing towards the -y axis. I attached a
small picture to make it clearer. So here are some of my questions.

What should the "vu" be at the daylight matrix? I am not sure which axis
of the BSDF corresponds to the "vu". My guess is that "vu" should be 1,
1, 0 or 1, -1, 0? Should the pipe model from which I generate the BSDF be
correctly oriented as well?

Is there any way to have the model of the room oriented towards the north
(y axis) and then set the correct orientation via the "vu" or some other
way?