[Radiance-general] Rendering large space with small detail (small picture now attached!)

Thu May 28 23:35:01 PDT 2009

Hi Jack,

Thanks for that tip, it seems to work. Reversing the normals was very easy,
I use Ecotect as the CAD interface to radiance and it was just a case of
selecting the object and hitting 'cntrl R'.

I'll be running the simulation over the weekend with the new glow surfaces
in replacement of the lights to see how much quicker it is.

As for you suggestions about ab, dj and ds parameters, I'll give them a try
separately once I have the glow sorted.

Thanks again,

Regards,

Paul.

On Thu, May 28, 2009 at 11:50 PM, Jack de Valpine <jedev at visarc.com> wrote:

> Hi Paul.
>
> Since a glow functions like a light source the material is sensitive to the
> orientation of the normal for the "glowing" polygon geometry. Thus when a
> glow material such as:
>
> void glow test.glow
> 0
> 0
> 4  1 1 1 0
>
> is applied to a polygon, the "front" side of the polygon (eg, the positive
> normal) will glow with a radiance of 1 (in the above case) whereas the
> backside of the polygon (the negative normal) will appear black.
>
> So in your case any polygons that appear black need to be re-oriented, so
> they glow in the right direction. There are a couple of ways to check and
> fix this. The way we usually check is to apply a glow material to the
> selected geometry and then objview just the selected geometry. This way we
> can do a quick visual check. Now if you are lucky, all the geometry either
> points in the right direction or it does not. If this is the case and all
> the geometry is black, then you can do:
>
> xform -I original_geometry.rad > original_geometry.flipped.rad
>
> This will flip the orientation of all the normals in original_geometry.rad.
> If on the other hand there is a mix of glowing and black polygons then you
> will have to go back into your modeling application and figure out how to
> flip things either by rebuilding the geometry or some other strategy. In
> Autocad (for example) 3dfaces that are built in a clockwise manner will have
> the normal pointing out of the clockwise face (I hope I am remembering this
> correctly).
>
> The fourth argument of a glow specifies a sphere of influence for the glow,
> resulting in illumination localized within the specified radius (the fourth
> argument is the radius in the model units within which the glow will
> essentially act like a light). So in other words a glow can actually be used
> to illuminate things. So you should be thoughtful about how you specify this
> value, to little and things may not be illuminated locally (if they need to
> be at all), to big and you basically have another light source in the scene.
> I think that Andy suggested you could break the scene down between interior
> electric lighting and various daylighting scenarios, with results being the
> combination of electric plus the desired daylighting. You can probably go
> one step further and break out the glow related "lighting" and run that
> separately. The thinking would be that this would allow you to test and tune
> your glow materials if that makes sense.
>
> More generally there are a couple of other items to consider. By using
> mkillum you have essentially "moved" the resulting light into the space,
> because of this you may be able to use a lower -ab setting such as -ab 1. On
> the other hand, if some of your illum surfaces span large areas, you will
> need to set  -ds (direct sampling) to subdivide these surfaces essentially
> "spreading" the light out over the surface rather than samping the middle of
> the polygon. You may also need to experiment with -dj (direct jitter).
>
> I hope this helps.
>
> Regards,
>
> -Jack de Valpine
>
> Paul Chilton wrote:
>
>   Hi Rob, Andy,
>
> Thank you both for you suggestions. I've been concentrating on getting the
> glow material to properly work first.
>
> I've looked at the Radiance reference manual and read the description of
> glow. In my rad file I've made a new glow material:
>
> *void glow* glowsurface
> 0
> 0
> 4 0.898 0.898 0.898 50
>
> and I've changed the name of the polygon that I want to glow from it's
> original surface name of 'plaster_insulated' to the name specified above
> i.e. 'glowsurface'. However in my image the surface appears to be black and
> I've tried changing the maxrad variable but this hasn't had an effect. I've
> read what it says about maxrad but I'm still unsure of what it is
> exactly and what the variable range is (is it a 0-1?) and what a typical
> value is.
> Could you please help?
>
> Regards,
>
> Paul.
> On Wed, May 27, 2009 at 3:08 PM, Rob Guglielmetti <rpg at rumblestrip.org>wrote:
>
>>
>> On May 26, 2009, at 8:07 PM, Paul Chilton wrote:
>>
>> Hi Lars, Rob
>>>
>>> It looks like I have managed to get the mkillum surface to work for the
>>> skylight. The render times are reduced and the images displayed look
>>> different too.
>>>
>>> However, I have been testing the use of the mkillum without the
>>> artificial lighting turned on in my model. When I do turn them on and run
>>> them with the parameters set to high accuracy levels, the simulation takes a
>>> very long time. I think that any time gained by the mkillum surface is
>>> negated by the number of lights it has to simulate.
>>>
>>
>> The simulations will increase as you increase the number of light sources,
>> that is a fact of life (or virtual life, as in this case). The mkillum
>> process will help improve the speed and accuracy of the lighting simulation
>> of the light filtering in from the skylight, but as you add in complexity
>> through electric light sources, you will experience a delay in the
>> simulation times, yes.
>>
>>
>> Is there a way of simplifying the artificial lighting of the tenants
>>> either side of the mall space? The goal of the artificial lighting in the
>>> tenancies is not to be highly accurate but rather to give the daylight in
>>> the mall space some context and to make it look more realistic as I’m only
>>> concerned about the daylight in the mall. Ideally I would like to put a
>>> mkillum surface in the position of the array of lights but I feel that this
>>> wouldn’t help reduce the complexity of the simulation as the same number of
>>> calculations still need to be carried out, am I right?
>>>
>>
>> The electric lights probably aren't doing much in terms of contribution to
>> the overall lighting that is predominantly from the skylight. In this case
>> you can use the glow material for your lights (with a small radius, see the
>> docs) to affect a visual context as you are looking for without exacting a
>> huge penalty on the render time.
>>
>>
>>> Is there a way in Radiance to make a planer object emit a certain amount
>>> of uniform light?
>>>
>>>
>> Yep, the glow is the material you want for this. I have used it
>> infrequently but I believe this is exactly what you need to get these
>> renderings looking good and completing in reasonable timeframes.
>>
>> - Rob Guglielmetti
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>>
>
>
>
> --
> Paul Chilton
>
> Renewable Energy Engineer
>
> [m] 0400 306 791 | [e] p.chilton at gmail.com
>
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>
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>
> --
> # Jack de Valpine
> # president
> #
> # visarc incorporated
> # http://www.visarc.com
> #
> # channeling technology for superior design and construction
>
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>

-- 
Paul Chilton

Renewable Energy Engineer

[m] 0400 306 791 | [e] p.chilton at gmail.com
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