It's an interesting thought; I am interested in values rather than images though.
The spherical sensor approach seems the best for what I am trying to achieve, so I'll see if I manage to implement that, otherwise the composite cubical sensor is the short and dirty road...
My initial confusion was because I initially thought that 6 right angle sensors would have given me a perfectly spherical sampling of the space, now I understand that's not the case and how to go about this.
Thanks everybody for the ideas and guidance,
From: giulio antonutto [mailto:firstname.lastname@example.org]
Sent: 09 May 2012 08:55
To: Radiance general discussion
Subject: Re: [Radiance-general] integral of radiation in one point-spherical illuminance
I think there is another way, which requires some more fiddling, but that can give you a lot more flexibility.
Especially with visualisations.
I would start by taking n. 6 x 90º wide angular images of luminance from the observer position.
You could use vwrays to work with rtrace.
Then derive the illuminance at the view point, as you know the solid angle of each pixel / direction and the luminance of it.
See the IESNA book for details. You could write a little script with rcalc, python or octave.
I guess Andy or Greg would do all in one line with sed / awk
Once done you could have polar maps of your illuminance component, directionality of lighting in the space, etc etc.
To start playing with the idea you could do as Mark is suggesting, 6 illuminance values are good as you could easily plot the vector illumiannce to visualise the directionality of lighting.
This is an useful metrics for museums.
Either way, have fun!
On 8 May 2012, at 14:16, Giovanni Betti wrote:
Dear Martin, Minki,
Thanks for the replies, I guess what I was trying to calculate (and to whom dr. Martin refers to) is better called cubical illuminance; the script Greg shared with Minki (thanks as always, Greg!) allows to sample a full sphere in one go.
I think I have my ideas a lot clearer now, I'll just need to implement either one of the approaches.
From: Moeck, Dr. Martin [mailto:email@example.com]
Sent: 08 May 2012 12:52
To: 'Radiance general discussion'
Subject: Re: [Radiance-general] integral of radiation in one point -spherical illuminance
that is called spherical illuminance. As an approximation, you could calculate 6 illuminance values (up, down, East, West, North, South) and average them. Christopher Cuttle wrote a few papers on spherical illuminance.
From: Giovanni Betti [mailto:firstname.lastname@example.org]
Sent: Tuesday, May 08, 2012 1:42 PM
To: Radiance general discussion
Subject: [Radiance-general] integral of radiation in one point
I have question that I hope you'll help get my head around.
I want to calculate the overall illuminance on a point in space that is, regardless of directionality.
I have made some simplified 2d sketches for clarity.
As I understand a radiance sensor point in rtrace will have cosine related sensitivity (image01)
If I am to place two coincident with opposing normals (image2) I'll miss on contributions from the sides.
Rotating the normals by 90 degrees at a time (figure 3) and summing contributions might not work either because will overestimate diagonal contributions (figure 4 ).
So I'm not getting too much closer to the solution...
Is there something that I am missing here?
Any light on this will be appreciated,
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