[Radiance-general] advice for material modeling

[Jack de Valpine]

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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