[Radiance-general] Three-Phase Method - subdivision of window with sensor located close to the window

[Andy McNeil]

Hi Anne,

On my computer the text on your charts show up as black squares.  But I think I can still provide some relevant advice.

Generally speaking, subdivision of the window for the three phase method is only necessary when there are nearby external obstructions or for intermediary blind positions.  But your case is unusual - your sensor point is so very close to the window.

When generating the view matrix we typically use a light material for the window.  Direct (deterministic) sampling is used to calculate the window's contribution.  The direct sampling algorithm will automatically divide a light source according to the -ds parameter, however the maximum number of divisions is limited to 64 (as determined by the variable MAXSPARTS in source.h).  Given the proximity of your sensor to the window I don't think 64 direct samples will accurately map the window's outgoing klems divisions to illuminance contribution at your sensor.  Manually subdividing the window is one approach.  Though rather than horizontal bands I'd suggest a pattern of squares that is finer near the sensor and corse away from the sensor (see ascii art below).  You also want to set -dt 0 and -dc 1. 
____________________
|              |__|__|__|              |
|______|__|__|__|______|
|              |                |              |
|______|_______|______|

Alternatively you could consider using ambient sampling to sample the window.  You could try using a glow material for the window and set -ad 2000 or higher.  Roughly half the initial ambient sample rays would hit the window (because your sensor is nearly against the window).  -ab can be low and -lw should be less than 1/ad, probably 1/ad^2.   I've never tried this, so I don't know how well (or if) it'll work.

If it were me, I'd give the glow material a try.  It seems much more elegant and now that I think about it, it might be a better approach for some spaces.

Good luck,
Andy




On Apr 28, 2011, at 8:48 AM, Anne Iversen wrote:

> Hi list - Hope you have time to give me some guidance here :-)
> 
> 
> 
> My question is if any of you have any recommendations or thoughts on how I should or shouldn't subdivide the window?
> 
> 
> 
> Problem:
> 
> I have a scene with a sensor located close to the window. The window is placed in y=0.82, and the sensor is located in y=0.84, just behind the window. Due to the sensor location this close to the window I’m thinking I have to subdivide the window to get a correct sensor reading, especially when solar shading is included in my simulations.
> 
>  
> I have run simulations for 4 different cases with different subdivisions of the window. The transmission matrix is an .xml file generated with window6 for a clear window. Nothing special here, yet! In further simulations I’ll introduce solar shading.
> 
> My simulation results show that the sensor signal differs with the different subdivisions.
> 
> You can see the results and subdivision of window in this link:
> http://dl.dropbox.com/u/9713279/ThreePhaseMethod_Subdivision.pdf
> 
> And my script if necessary, in this link:
> http://dl.dropbox.com/u/9713279/threephasemethod.bash
> 
> Thanks in advance,
> Anne
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