[Radiance-general] BSDF xml into Radiance

[Gregory J. Ward]

Hi Dan,

If you want your sensors averaged over some small area (rather than measured at a point), then you can jitter the sample location.  Otherwise, just repeat the point value N times corresponding to your -c argument.

-Greg

> From: "Daniel C. Glaser" <daniel at lightfoundryllc.com>
> Date: July 25, 2012 3:10:36 PM PDT
> 
> Dear Greg,
>  Thank you for letting us know about the -c option.  I am going to try it with rtcontrib (sensors) and wanted to ask for advice on how to setup the points for averaging.  For example, if I choose 4 for -c, do I send in the same point 4 times or is there a heuristic for perturbing or regularly spacing these points for improving results?
>  Thanks for creating this feature!
> 
> - Dan
> 
> On 7/25/2012 10:44 AM, Greg Ward wrote:
>> Hi Lars,
>> 
>> Andy probably is the right person to respond to this, but as he's on a vacation until the end of the month, I thought I'd offer a couple of comments (inline).
>> 
>> Cheers,
>> -Greg
>> 
>>> From: "Lars O. Grobe" <grobe at gmx.net>
>>> Date: July 25, 2012 1:18:42 AM PDT
>>> 
>>> Hi Andy, hi list-subscribers,
>>> 
>>> I just came across this recent message about the usability of the bsdf
>>> material type with patch-based models of the sky including direct sun
>>> and complex fenestration. To avoid misunderstandings, I will try a short
>>> summary for others to comment on available options for annual
>>> simulations with complex glazing:
>>> 
>>> 
>>> 1) classic radiance tools (rpict, rtrace), complemented by mkillum to
>>> relax ambient setting.
>>> 
>>> Advantages: low noise, validated.
>>> 
>>> Disadvantages: very slow for annual simulations, no support when
>>> non-planar specular reflective surfaces are involved.
>> More specifically, non-planar, specular reflectors run into trouble for insolation.  Cloudy skies or sunless skies are no problem.
>> 
>>> 2) rtcontrib and patch-based model.
>>> 
>>> Advantages: faster for annual simulations.
>>> 
>>> Disadvantages: noise, nice images require high (slow) -ad and cannot be
>>> optimized using mkillum, limitations about specular non-planar
>>> reflectors apply.
>> The accuracy of non-planar, specular reflectors is actually better than #1, but the results are somewhat noisy.  A new -c option to vwrays (coupled with the rtcontrib -c option) is a good way to reduce noise that is available in the latest HEAD.  This is a better way to reduce noise than increasing -ad, and less costly.
>> 
>>> 3) rtcontrib and patch-based model, bsdf.
>>> 
>>> Advantages: support for non-planar reflectors, should be slightly faster
>>> than 2) as the fenestration system does not have to be traced internally
>>> - did anyone compare?
>>> 
>>> Disadvantages: still high -ad settings required leading to extended
>>> rendering times and still no way to get mkillum in, tends to
>>> underestimate direct sun (according Andy's message).
>>> 
>>> 
>>> 4) three-phase-method.
>>> 
>>> Advantages: very fast, can also be used with non-planar specular
>>> reflectors as bsdf data is supported.
>>> 
>>> Disadvantages: requires quite a lot of set-up work, e.g. subdivisions to
>>> reflect external obstructions. Patches visible in the results,
>>> fenestration geometry is not visible.
>> Andy has proposed an improved annual simulation method, which we hope to work on next year, to remedy the direct solar sampling difficulties in the 3-phase method.  It should also alleviate problems with external facade geometry and reduce the need to subdivide windows.
>> 
>>> 5) pmap.
>>> 
>>> Advantages: can be used with non-planar reflectors and multi-peak
>>> transmission.
>>> 
>>> Disadvantages: unknown status (any news?), not integrated with rtcontrib
>>> (contributions would need to be rendered manually).
>>> 
>>> 
>>> So if I need a way to generate images with visible fenestration
>>> geometry, the only reliable option would be 2), which requires very
>>> hight settings for -ad and thud will still be rather time-consuming, if
>>> noise is to be controlled.
>>> 
>>> Cheers, Lars.
>>> 
>>> On Tue, 2012-06-12 at 08:43 -0700, Andrew McNeil wrote:
>>> 
>>>> Though I've found that the BSDF material doesn't work well for
>>>> daylight coefficient based annual simulations (I'm assuming dds.bash
>>>> is a dynamic daylight simulation script).  Putting the solar radiance
>>>> into skypatches relies on probabilistic sampling to find patches
>>>> containing the sun, and if you don't have much direct transmission
>>>> from the direction of the sun, you aren't likely to find the sun.  Not
>>>> finding the sun causes big errors.
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>> 
> 
> 
> 
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