[Radiance-general] Ambient exclude transfomed material in instances

[Jack de Valpine]

Hi Iebele,

To use local u,v coordinate mapping (Lu,Lv) you need to use obj2mesh 
rather than obj2rad.

Here is the process for making a mesh element:

    Define mats.tree.rad using simple materials first as an example. The
    names of the materials must correspond to the names of the materials
    indicated for the .obj geometry (take a look in the .mtl file to get
    the names).

        mats.tree.rad:

            void plastic Bark
            0
            0
            5 1 1 1 0 0

            void plastic Leaf
            0
            0
            5 1 1 1 0 0

    Generate tree.rtm as follows:

        obj2mesh -a mats.tree.rad tree.obj > tree.rtm

    Creat tree.mesh.rad as follows:

        tree.mesh.rad:

            void mesh tree
            1 tree.rtm
            0
            0

    Test you mesh:

        objview tree.mesh.rad

Now lets apply more complex materials using local u,v coordinate 
mapping. To do this you need the following image data:

       1. bark.pic
       2. aspect ratio for bark.pic (y/x), lets call it <arB>
       3. leaf.pic
       4. aspect ration for leaf.pic (y/x), lets call it <arL>
       5. leaf.matte.pic - this is the alpha/matte channel for the leaf.
          The correct way to setup the matte is  for white to represent
          the leaf and black to represent what is not the leaf. This
          means that you may have to invert the matte the comes from xfrog.

    Now lets create the complex materials in mats.tree.rad

        mats.tree.rad:

            #BARK definition
            void colorpict bark.tile
            7 red green blue Bark.pic . frac(Lu) frac(Lv)*<arB>
            0
            0

            bark.tile plastic Bark
            0
            0
            5 1 1 1 0 0

            #LEAF definition
            void colorpict leaf.tile
            7 red green blue Bark.pic . frac(Lu) frac(Lv)*<arL>
            0
            0

            leaf.tile plastic leaf.map
            0
            0
            5 1 1 1 0 0

            leaf mixpict Leaf
            7 leaf.map void green leaf.matte.pic . frac(Lu) frac(Lv)*<arL>
            0
            0

    Now recompile your mesh:

        obj2mesh -a mats.tree.rad tree.obj > tree.rtm

    Now view it:

        objview tree.mesh.rad

You should add Bark and Leaf to your ambient exclude file/list if you do 
not want them in the ambient calculation. You can use tree.mesh.rad 
along with replmarks, xform or some other method to deploy the tree 
object in the scene.

This should work fine. Let me know if you have any questions.

-Jack

Gregory J. Ward wrote:
> Hi Iebele,
>
> I can't be much help on this, as I'm not familiar with the model, but 
> the general idea with local coordinates is that you don't have to do 
> the mapping yourself.  It's supposedly handled by the mesh generation 
> software, and isn't affected by transformations as a global coordinate 
> mapping would be.
>
> I hope this is a helpful clue, as it's about all I have to offer.
> -Greg
>
>> From: iebele <info at iebele.nl>
>> Date: April 3, 2007 8:39:12 AM PDT
>>
>> Thanks Greg an Jack for your excellent and very  helpfull suggestions.
>>
>> I now have succesfully converted the .obj file to rad, using obj2rad 
>> ( polytrans did indeed work with Xfrog obj-files, but meshlab did not 
>> accept these files Lars ).
>>
>> However I can't get the mapping right. I've tried a lot, but with no 
>> succes. Would you please share with me an example of the materials 
>> you use for the bark and the leaves?
>>
>> I just don't really understand when and how to use Lu and Lv  or 
>> frac(Lu) and frac(Lv) in the colorpict modifier and how these can 
>> ever be placed  in a reasonable way on each triangle in the output of 
>> obj2rad, which in my case is like :
>>
>> leaf_col_leaf2 polygon leaf22836.60976
>> 0
>> 0
>> 9
>>         -0.250204           0.195593             13.838
>>          -1.00383          -0.956752            13.8816
>>          -1.21881           -0.19178            13.5622
>>
>> I never really understood the meaning of texture-coordinates, but at 
>> this time I feel that is what  is  missing here.
>>
>> Is there a difference in using obj2rad and obj2mesh for this purpose 
>> ? I tried both but with the some odd results concerning the 
>> coordinate mapping.
>>
>> -Iebele
>
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>

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

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