[Radiance-general] daylight factor and rtrace cmd

[Compagnon Raphaël]

Hello

In fact your calculation seems absolutely correct.
You ask rtrace with options -I and -oodv this means the following:
  - radiance will place a virtual lambertain reflector at each point of your input file
  - for each point of your input file a ray will be traced from a virtual point 1 meter above in the vertivcal down direction
  - this is excatly what appears in the rtrace output you are providing. The "od" in -oodv means you ask rtrace to output 
    the x,y,z origin
    the x,y,z direction which is traced (you get 0 0 -1 in your output file)
 - each of these rays will find the virtual lambertain reflector at its first intersection
 - then radiance will compute the irradiance at this intersection point
 - and rtrace returns the irradiance value (the "v" in -oodv )

The rtrace -i behaves differently: rtrace will trace a ray for each input point in the specified direction. Then it will compute the irradiance at the first instersection point found in the scene. In your case, with the same input file you would get the irradiance on the ceiling... which is probably not what you really need.
This explains why the most useful -I option exists!

Raphael Compagnon

________________________________________
De : radiance-general-bounces at radiance-online.org [radiance-general-bounces at radiance-online.org] de la part de PAUPELIN-HUCHARD Valere [v.paupelin-huchard at elioth.fr]
Date d'envoi : jeudi, 16. juillet 2009 18:17
À : radiance-general at radiance-online.org
Objet : [Radiance-general] daylight factor and rtrace cmd

Hello,

I'm trying to do daylight factor calculation. I am observing a 1 meter height offset between my workplan point file which is already at 0.85m above the floor (*.fld) and the rtrace result (*.irr).
Someone would tell me why?

the command used is:
rtrace -ab 7 -ad 2048 -oodv -I rcp.oct<numeric/plan_de_travail.fld>numeric/090715_BU_Rennes_07_vitrage_irradiance.irr

four first lines sample of the files:

plan_de_travail.fld:
x          y         z         o
0.50     -0.25     1.84     0 0 1
0.50     0.00      1.84     0 0 1
0.50     0.25      1.84     0 0 1
0.50     0.50      1.84     0 0 1

090715_BU_Rennes_07_vitrage_irradiance.irr
x                        y                        z                          o                                                                          r                         g                         b
5.000000e-001    -2.500000e-001     2.840000e+000     0.000000e+000 0.000000e+000 -1.000000e+000     1.406147e-001     1.406147e-001     1.406147e-001
5.000000e-001     0.000000e+000    2.840000e+000     0.000000e+000 0.000000e+000 -1.000000e+000     1.581891e-001     1.581891e-001     1.581891e-001
5.000000e-001     2.500000e-001     2.840000e+000     0.000000e+000 0.000000e+000 -1.000000e+000     1.765201e-001     1.765201e-001     1.765201e-001
5.000000e-001     5.000000e-001     2.840000e+000     0.000000e+000 0.000000e+000 -1.000000e+000     1.890535e-001     1.890535e-001     1.890535e-001

I am afraid my daylight factor result are not valid at the height of 1.84m but at 2.84m, am I wrong?

Thanks,
Valere.