[Radiance-general] Re: advice for material modeling

[R Fritz]

It's an ideal "crowdsourcing+research" problem, but it still needs some 
staffing. Maybe, if I can get some funding...

On 2010-04-27 10:44:31 -0700, Jack de Valpine said:

> Hi Dan,
> 
> There have been questions and discussions on a material database. But I 
> think that given the quantity and variety of materials out there this 
> quickly gets out of control. Consider glazing alone with something like 
> Optics5  (a complete software package!) for dealing with this class of 
> materials.
> 
> Perhaps another way to consider the forest is by estimating an average 
> transmittance and then just using a trans material. One could even vary 
> this over some vertical dimension.
> 
> Best,
> 
> -Jack
> 
> 
> Dan Glaser wrote:
>> Dear Jack and Lars,
>> Thank you very much for the timely modeling advice-- yes, I can see how 
>> calibrating the photographs can help with selecting the right color for 
>> the stone and brick.  Also, thanks for the tips on color variation 
>> strategies.
>> I will let you know what I come up with for the texture.  I know its a 
>> cross between an art and a science in doing so (e.g. see the "forest" 
>> example below)-- just thought maybe someone have studied this material 
>> before.  On a related note, have there been discussions on having a 
>> material database at radiance-online/elsewhere? On a project where I 
>> had to quickly model how a forest would impact the lighting on a 
>> facade, I hacked perforate.cal instead of trying to model the actual 
>> trees (trunks, branches, needles, yuk).
>> 
>> This was the real scene:
>> 
>> http://www.lightfoundryllc.com/materials/forest/forest.jpg
>> 
>> and this was what was modeled:
>> 
>> http://www.lightfoundryllc.com/materials/forest/model.jpg
>> 
>> and the script I hacked:
>> 
>> http://www.lightfoundryllc.com/materials/forest/forest.cal
>> 
>> Given more time I would have tried to increase the density of the dot 
>> pattern near the ground/etc.
>> - Dan
>> 
>> 
>> 
>> On 4/26/2010 10:05 AM, Jack de Valpine wrote:
>>> Hi Dan,
>>> 
>>> I just got back in and see that I missed this so perhaps my reply is 
>>> too late to be of use. In any event here are a few thoughts.
>>> 
>>> If you want to create "high quality" renderings then the best thing to 
>>> do is to obtain some good photographs of these materials. I know that 
>>> this can be a challenge as it means that you have to be much more 
>>> demanding with the client in terms of the information that they need to 
>>> provide, such as access to decent samples, but it can definitely be 
>>> worth it. In my experience the best thing to do is to shoot your own 
>>> photos of good samples and calibrate with the Macbeth Color Checker (or 
>>> some other mechanism for calibrating reflectance and color). That way 
>>> you have control over everything. On the other hand if you could 
>>> perhaps get representative photos from the stone supplier then you 
>>> could perhaps use these to develop image patterns that can be adjusted 
>>> to the estimated reflectance information that you do have. Note though 
>>> if you want the rough surface of the materials to cast shadows 
>>> depending on how the light is hitting the surface (time of day 
>>> perhaps), then you will have to use actual geometry, which is going to 
>>> be a lot more complicated.
>>> 
>>> Again depending on your rendering/visualization goals and if it just is 
>>> not possible to get good photos, another approach is to consider what 
>>> is important to demonstrate given the possible view(s) that you will be 
>>> showing. For stone masonry materials the first thing that I always 
>>> consider is how much variation is there from stone to stone. My guess 
>>> is the sandstone is supposed to have relatively low variation, whereas 
>>> the brick seems to have quite a high degree of variation. This kind of 
>>> variation can be accounted for procedurally with a tiling function that 
>>> varies the brightness and/or color of the tile (stone unit). Another 
>>> item to consider at this macro level is the relative reflectance of any 
>>> mortar or joint condition, this again can be treated as part of a 
>>> procedural tiling function. With these two items accounted for the next 
>>> thing to try to approximate to some level is variation within a given 
>>> stone unit. This is where things get a bit more challenging with the 
>>> materials you are looking at. The sandstone can probably be 
>>> approximated with some variation of noise functions. The brick though 
>>> demonstrates some pretty sharp cutoffs in variation and color which I 
>>> am not sure offhand how I would treat. Just to get the variation it 
>>> might be worth searching for imagery online and seeing if there is 
>>> something that you could use to get the variation.
>>> 
>>> Hope this helps.
>>> 
>>> Regards,
>>> 
>>> -Jack de Valpine
>>> 
>> 
>> 
>> --
>> LF logo 	Daniel C. Glaser, PhD, LEED AP
>> Principal
>> Light Foundry, LLC
>> T: 510.387.8890 | F: 315.410.2617
>> www.lightfoundryllc.com <http://www.lightfoundryllc.com>
>> 
>> 
>> 
>> 
>> 
>> 
>> 
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-- 
Randolph Fritz