# RE : daylight factor and rtrace cmd

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 : [email protected] [[email protected]] de la part de PAUPELIN-HUCHARD Valere [[email protected]]
Date d'envoi : jeudi, 16. juillet 2009 18:17
À : [email protected]
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.

rtrace -oodv has nothing to do with the "1 meter offset". In fact the "1 meter offsett" thing is just related to how the rtrace -I command computes irradiance at the points and in the directions specified at the input.

Raphael

···

________________________________________
De : [email protected] [[email protected]] de la part de Guglielmetti, Robert [[email protected]]
Date d'envoi : jeudi, 16. juillet 2009 20:09
À : Radiance general discussion
Objet : RE: [Radiance-general] daylight factor and rtrace cmd

-----Original Message-----
From: [email protected] [mailto:radiance-
[email protected]] On Behalf Of Compagnon Raphaël
Sent: Thursday, July 16, 2009 11:30 AM
To: Radiance general discussion
Subject: RE : [Radiance-general] daylight factor and rtrace cmd

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!

Well now I've gone and confused everyone. You are right, -i (lowercase) is used for picking out illuminance at scene points, and so works as Raphael has described. -I (uppercase) is what I normally use for computing illuminance at a point. I simply use -I with -ov which gives me illuminance at that point. I have not used those other output fields and I'm still a little confused as to how this "1 meter offset" happens with -oodv.

Here's a thread-concluding post from a couple years ago that I have consulted in the past:

http://www.radiance-online.org/pipermail/radiance-general/2007-March/004213.html

- Rob

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

sorry, little time - may be not the answer you are looking for, but as Raphael says, nothing to do with it.
anyway if you want a point and the illuminance at that point in the output file,
use that point in the grid, -I in rtrace and again -opv.
this saves the point from the grid to the final output.

explanation, the point of the grid is the intersection point in the calcualtion as the observer is moved 1 unit from it and used to trace a luminance calculation converted in illuminance...
anyway
-opv

ciao
G

--- Gio 16/7/09, Compagnon Raphaël <[email protected]> ha scritto:

···

Da: Compagnon Raphaël <[email protected]>
Oggetto: RE : [Radiance-general] daylight factor and rtrace cmd
A: "Radiance general discussion" <[email protected]>
Data: Giovedì 16 luglio 2009, 20:30

rtrace -oodv has nothing to do with the "1 meter offset". In fact the "1 meter offsett" thing is just related to how the rtrace -I command computes irradiance at the points and in the directions specified at the input.

Raphael

________________________________________
De : [email protected] [[email protected]] de la part de Guglielmetti, Robert [[email protected]]
Date d'envoi : jeudi, 16. juillet 2009 20:09
À : Radiance general discussion
Objet : RE: [Radiance-general] daylight factor and rtrace cmd

-----Original Message-----
From: [email protected] [mailto:radiance-
[email protected]] On Behalf Of Compagnon Raphaël
Sent: Thursday, July 16, 2009 11:30 AM
To: Radiance general discussion
Subject: RE : [Radiance-general] daylight factor and rtrace cmd

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!

Well now I've gone and confused everyone. You are right, -i (lowercase) is used for picking out illuminance at scene points, and so works as Raphael has described. -I (uppercase) is what I normally use for computing illuminance at a point. I simply use -I with -ov which gives me illuminance at that point. I have not used those other output fields and I'm still a little confused as to how this "1 meter offset" happens with -oodv.

Here's a thread-concluding post from a couple years ago that I have consulted in the past:

http://www.radiance-online.org/pipermail/radiance-general/2007-March/004213..html

- Rob

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general