[Radiance-general] advice for material modeling

[Dan Glaser]

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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