Question about the use of xform in a exercise in the radiance_cookbook

radiance-general
1

Hi everyone,

I am following the radiance_cookbook.pdf to learn about radiance. But for the exercise at p12: there is a exercise to use xform command to a array of fittings:

$ cat lights.rad
!xform -t 1 1 2.95 -a 3 -t 1 0 0 -a 4 -t 0 1 0 erco.rad

I know that the -a 3 -t 1 0 0 -a 4 -t 0 1 0 is used to place fitting. But I am confused about why use -t 1 1 2.95 to translate the scene. Dose this is used to define the original coordinate of the fitting array, like z= 2.95 is the height of working plane, x=1 and y=1 is the original position of the fitting array?

Cheers,

Hao

2

Hi Hao,

The xform line you’re showing is a little complicated, because it creates a 3x4 array. Why not break it down?

Start with only

!xform erco.rad

in your lights.rad file. Visualise it and see what it does. Next, try

!xform -t 1 1 2.95 erco.rad

Again, visualise and see what happens

!xform -t 1 1 2.95 -a 3 -t 1 0 0 erco.rad

and so on…

A

3

Hi Alex,

Thanks a lot for your help. In fact, I tried to visualize them before. Based on the visualization, I believe what I understood at the beginning is right.

Cheers,

Hao