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

[Paul Chilton]

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.

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?

Is there a way in Radiance to make a planer object emit a certain amount of
uniform light?

Look forward to hearing from you,

Paul

On Wed, May 20, 2009 at 2:09 PM, Rob Guglielmetti <rpg at rumblestrip.org>wrote:

> On May 19, 2009, at 8:09 PM, Paul Chilton wrote:
>
>> In the .rif file, I'm creating the mkillum function which I've used the
>> tutorial example is; mkillum= -av 18 18 18 -ab 0 . I then go into the .rad
>> file to find the properties and geometry of the skylight and then copy and
>> paste those values and descriptions separately into a new .rad file and save
>> it as window.rad. In the .rif file I then refer to this window.rad file by
>> specifying illum= window.rad. My interpretation of this procedure is that
>> rather than the ambient being the generator of light into the space it is
>> now the window itself which is the light source.
>>
>
> Hi Paul,
>
> So you're on your way. Lars has explained that mkillum will do the
> "bringing of the direct component closer to your scene" as I suggested. A
> couple of other pointers:
>
> You want to create impostor geometry or define your skylight apertures as
> illum sources. You do this by adding "illum=" lines to the .rif file. Let's
> say you have a skylight defined by a skylight.rad file, that describes the
> polygons that make up the skylight opening; you would remove that reference
> from the "scene=" line(s) and add an "illum=" line. You are telling rad to
> take any polygons defined in the illum= files and do a backwards raytrace
> from those polygons and out into the scene beyond. Generally this is the
> exterior environment, and as such the rays traced stand a much better chance
> of hitting the sun. The results of this raytrace operation are saved and
> applied as a data file to the polygons defining the skylight or aperture and
> that aperture becomes a light source. I would not worry about an -av value
> for your mkillum= line, but I would definitely increase the -ab value to 2
> or 3, and -ad 512.
>
> You should not do anything to the .rad files from there. rad is great; if
> you tell rad (via the illum= line(s)) which surfaces should be precalculated
> as light sources, rad will manage the creation of these secondary light
> sources as they are called and create its own separate rad files that
> substitute the precalculated illums for the calculations and/or renderings.
> Definitely look at the rad manual page for more info on this...
>
> - 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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