[Radiance-general] Five-phase Method: Proxy Geometry and BSDF material type

[Alireza Hashemloo]

Andy and Rob,

Thank you very much for you responses. I think it is now more clear for me
why I should opt for two coincident glazing polygons for the view and
daylight matrices or two separate ones with a gap between them depending
on my simulation scene and the type of BSDF data I will be using.

Best Regards,
Alireza

On Sun, Jan 31, 2016 at 12:00 PM, Andy McNeil <mcneil.andrew at gmail.com>
wrote:

> Alireza - Five great questions.
> Rob - Five great responses.
>
> I've done these simulations with and without spacing. There are probably
> examples I've produced of both ways floating around. So I'll try to explain
> why you'd want to do it one way or the other.
>
> The basic idea is to make sure that you account for the window thickness
> and edge condition once and only once in your simulation. The genBSDF
> tutorial touches on the difference between a system specific BSDF, which
> includes edge conditions, and an infinite layer BSDF, which has no edge
> conditions. If your BSDF does not include the edge condition, then you want
> your sending and receiving surfaces to be coincident, so that the edge
> condition is accounted for in the view and daylight matrices. If your BSDF
> does include the edge conditions, then you want a space between your
> sending and receiving surfaces so that the edge condition is not duplicated
> in the view and daylight matrix.
>
> So how do you know whether you have an infinite layer BSDF or a BSDF with
> edge conditions?
> If your BSDF is generated by Window then it is an infinite layer, without
> edge conditions.
> If your BSDF is generated by genBSDF then it contains edge conditions,
> unless you took care to minimize sampling of edges (see genBSDF tutorial).
>
> If you're using proxied geometry, than your sender and receiver geometry
> needs to be spaced (the thickness of the geometry) so you should make sure
> that your BSDFs contain the edge effects.
>
> For the 5-phase method, your strategy starts with what you want to do for
> the direct sun coefficient matrix.
> If you want to use proxied geometry than the sender and receiver must be
> spaced apart and the BSDF should include edge effects specific to your
> model.
>
> If you want to use a tensor tree BSDF, then it depends on what you did to
> create the BSDF. If it is a typical genBSDF tensor tree run, then edge
> conditions are included in the BSDF and you should include a space between
> your sending and receiving surfaces. If however you took care to create an
> infinite layer BSDF (tensor tree) with genBSDF then your sender and
> receiver surfaces can be coincident.
>
> Hopefully this gives a little bit of backgroud to the whole space or no
> space between sending and receiving surfaces.
>
> Best,
> Andy
>
>
>
> On Sun, Jan 31, 2016 at 8:40 AM, Rob Guglielmetti <
> rob.guglielmetti at gmail.com> wrote:
>
>> Lots of questions, I think I can answer some of them…
>>
>>
>> >
>> > 1- In the tutorial, a single polygon (relative to the outline of the
>> glazing surface) is modeled in the scene at the exterior side of the
>> window. This polygon is referenced to generate the daylight matrix. A
>> second polygon is modeled in the scene on the interior side of the window
>> and it is referenced to calculate the view matrix.
>> >
>> > I was wondering if I could generate two identical co-planar polygons
>> where the normal vector of one polygon is looking at the interior side  and
>> the normal vector of the other polygon looks at the exterior side to be
>> referenced, respectively, for the view matrix and daylight matrix
>> calculations? if so, would it still be necessary to model the thickness of
>> the walls hosting fenestration systems in the simulation scene?
>>
>>
>> You could do that, just make sure that your octrees for the view and
>> daylight matrices only contain one the other polygon. If you have a
>> coincident pair of polys in the same octree, it’s up to chance which one is
>> hit by each ray traced. It’s already critical that every ray be counted
>> toward something meaningful (this is the reason for the phases in the first
>> place, with complex fenestration systems).
>>
>>
>> > 2- What is the "proxy geometry" in the five-phase method? is the "proxy
>> geometry" exclusively a reference to the polygon at the interior side of
>> the window system that is assigned a BSDF material?
>> > or is the "proxy geometry" a reference to the 3D geometry of the
>> venetian blinds (or any other type of shading layer of the fenestration
>> system) in the scene?
>>
>>
>> It’s the latter. That geometry serves to block the direct light, in that
>> phase of the workflow.
>>
>> >
>> > 3- what is the "thickness" as the first parameter in the Radiance BSDF
>> material type referring to? is it measured as the distance between the
>> daylight matrix polygon on the exterior side of the window and the view
>> matrix polygon at the interior side?
>>
>> Yes.
>>
>>
>> >
>> > or does "thickness" refer to the depth of the entire fenestration
>> system including the glazing panes and any shading layers?
>> >
>> > 4- If I model the mullions defining the edge condition of any
>> individual glazing pane in 3D scene, what would be the difference between
>> using LBNL's Window to generate a BSDF file and using genBSDF?
>>
>>
>> Hmm, I don’t think there would be a difference in terms of the Radiance
>> BSDF and calculations.
>>
>> >
>> > 5- What would be the difference between using a BSDF file based on
>> Klem's division scheme with higher resolution (where each Klem's patch is
>> subdivided to 4 new patches) and using a tensor tree BSDF?
>>
>>
>> The difference would be higher accuracy in the case of the tensor tree
>> BSDFs, at the expense of longer stimulation times, much larger files (both
>> the input and output), and longer BSDF generation times.
>>
>> - Rob
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