[Radiance-general] advice for material modeling

[Jack de Valpine]

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

-- 
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction



Dan Glaser wrote:
> Hi Everyone,
>   I am trying to model reddish "sandstone" as well as a brick called 
> "Navajo Gold."  The red sandstone has uneven, broken "layers" with 
> little bumps on its surface.  The Navajo Gold brick varies in color, 
> has tiny holes pocketing its surface, and also may not be flat.
>   Here is a link to an image of the sandstone:
>
> http://www.lightfoundryllc.com/materials/sandstone.jpg
>
>   And a few links to images of the Navajo gold:
>
> http://www.lightfoundryllc.com/materials/ng0.jpg
> http://www.lightfoundryllc.com/materials/ng1.jpg
> http://www.lightfoundryllc.com/materials/ng2.jpg
> http://www.lightfoundryllc.com/materials/ng3.jpg
> http://www.lightfoundryllc.com/materials/ngside.jpg
>
>  Unfortunately I do not have direct access to the materials, but 
> someone has measured their general reflectance values.
>   I would like to create a high quality rendering of an interior 
> curved wall made with red sandstone.  We are designing skylights for 
> accenting this wall for people outside to see (they would look through 
> a glass curtain wall to see it).  Ideally we would like to see little 
> shadows on the surface of the red sandstone due to its uneven layering 
> and some other effects due to its texture.
>   It would also be nice to have a good rendering of the Navajo Gold 
> brick walls, but this is less of a priority.
>   Can anyone give any advice for how to model the 
> pattern/textures/etc. for this or have pointers to success stories for 
> these types of materials?
>   Thanks!
>
> - Dan
>
>
> -- 
> 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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