[Radiance-general] Preview error - unknown object type "ashik2"

[Greg Ward]

Hmmm...  I guess it reflects about 22% more light, because of the way the specular reflectance reduces the effective diffuse reflectance in plastic2.  The total reflectance is about (1-.26)*.56+.26 for plastic2, and simply 0.56+0.26 for ashik2.

-Greg

> From: Georg Mischler <schorsch at schorsch.com>
> Subject: Re: [Radiance-general] Preview error - unknown object type "ashik2"
> Date: April 23, 2016 1:35:01 PM PDT
> 
> So does that mean that the right sphere in the slideshow reflects
> 26% more light on average than the left one?
> 
> void plastic2 mat1
> 4 0 1 0 .
> 0
> 6 .3 .7 .5 .26 .1 .02
> 
> void ashik2 mat2
> 4 0 1 0 .
> 0
> 8 .3 .7 .5 .26 .26 .26 150 5000
> 
> Its hard to tell from the images, but it does appear slightly brighter.
> 
> Cheers
> -schorsch
> 
> 
> Am 2016-04-22 23:15, schrieb Greg Ward:
>> Yes, unlike the other Radiance materials, you need to consider the sum
>> of specular and diffuse components to determine whether you are within
>> physical limits.  The standard "plastic" and "metal" (likewise
>> "plastic2" and metal2") simply make a binary choice between colored
>> and uncolored highlights.  The "ashik2" type allows you full control.
>> I don't know what materials this is useful, however.
>> Cheers,
>> -Greg
>>> From: Georg Mischler <schorsch at schorsch.com>
>>> Subject: Re: [Radiance-general] Preview error - unknown object type "ashik2"
>>> Date: April 22, 2016 1:31:40 PM PDT
>>> Very interesting, thanks.
>>> My conclusions go like this:
>>> * The useful range of the exponents seems to be between 0 (fully
>>> diffuse and 10000 (mirror-like). Between 5 and 100 looks like the
>>> most interesting range.
>>> * To create a plastic-like appearance, the specular reflection should
>>> be desaturated.
>>> * For a metallic appearance, the specular and diffuse reflections
>>> should have a similar tint.
>>> Remaining questions:
>>> * What happens when specular and diffuse colors are vastly different?
>>> I'm expecting something rather psychedelic... Do actual materials
>>> like that exist?
>>> * Do the diffuse and specular color values depend on each other?
>>> Eg. should their sum be less than 1?
>>> Cheers
>>> -schorsch
>>> Am 2016-04-22 17:10, schrieb Greg Ward:
>>>> Hi Schorsch,
>>>> The Ashikhmin-Shirley reflectance model is a kind of anisotropic Phong
>>>> model made physically plausible.  It's main advantage over the
>>>> standard anisotropic model in Radiance is that it includes a Fresnel
>>>> modifier, which I use for perfectly smooth surfaces.  Best to read
>>>> their original paper:
>>>> 	www.cs.utah.edu/~shirley/papers/jgtbrdf.pdf
>>>> I added this model to Radiance a few years back with help from Nicolas
>>>> Bonneel, as we were trying to run some comparisons.  Peter
>>>> Apian-Bennewitz also had requested it, so it seemed worthwhile to add.
>>>> Cheers,
>>>> -Greg
>>>>> From: Georg Mischler <schorsch at schorsch.com>
>>>>> Subject: Re: [Radiance-general] Preview error - unknown object type "ashik2"
>>>>> Date: April 21, 2016 10:34:16 PM PDT
>>>>> Is there any documentation on how to actually use this material?
>>>>> So far it is only mentioned in a release note and on some presentation
>>>>> slides, but not explained at all.
>>>>> What are eg. useful input values for "specular power"?
>>>>> Cheers
>>>>> -schorsch
>>>>> Am 2016-04-21 18:39, schrieb Greg Ward:
>>>>>> The '_unknown object type_' error is caused by reading in a frozen
>>>>>> octree (generated with "oconv -f") on an older version of Radiance,
>>>>>> before this type was added. You need to update your copy of Radiance
>>>>>> from https://github.com/NREL/Radiance/releases [1]
>>>>>> Chris has the right advice on X11.
>>>>>> Cheers,
>>>>>> -Greg
>>> --
>>> Georg Mischler  --  simulations developer  --  schorsch at schorsch com
>>> +schorsch.com+  --  lighting design tools  --  http://www.schorsch.com/
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> 
> -- 
> Georg Mischler  --  simulations developer  --  schorsch at schorsch com
> +schorsch.com+  --  lighting design tools  --  http://www.schorsch.com/
> 
> 
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