How to convert MERL brdf to Tensor-tree BSDF format?

radiance-general
1

Hi evreyone,

I am trying to convert “brdf data at MERL database” to “Tensor-tree BSDFs format”, but as I cannot find the details of the later format the conversion is not done yet.

For the “Matrix format”, I have already succeed in converting it and put them into tags. In this case, there is a table of “Matrix format”, so I can convert it.

Any help or advice would be appreciated.

Best,
Takushi

*Brdf at MERL is open brdf data taken for 100 samples. The link is bellow.
http://people.csail.mit.edu/wojciech/BRDFDatabase/brdfs/

2

Hi Takushi,

What you are attempting is difficult, but not impossible. The best reference I can offer for the tensor tree XML data may be found in the linked report.

The simplest thing to do would be to resample the data into a set of Shirley-Chiu subdivisions and employ the undocumented Radiance tool rttree_reduce to produce the data segment of a tensor tree XML file. The better-documented tool wrapBSDF can handle the details of the XML tags and format. You can look at the Perl script genBSDF.pl in src/util to learn more specifics about how these tools are used.

3

Hi Takushi,

while it may be not the most efficient approach, you should be able to
convert the MERL files into tabular data that pabopto2bsdf understands.
I have done that some years ago. Just be aware that the MERL data may be
out of range sometimes.

Best, Lars.

4

Dear Greg,

Thanks for your advice.
I read your linked report, and now succeed in resampling the MERL data to Shirley-Chui subdivisions.

The remaining challenge is to put them into curly braces.
If there is any document that explain the details of curly-braces rules, please refer to it.(I understood the overview by reading your linked report, but couldn’t get the details.)
“rttree_reduce” seems work for, but I hope the full-conversion consistently work in my own code.

Best, Takushi.

5

Dear Lars,

Thank you for your advice, and also telling what should be aware of.
I will look at “pabopto2bsdf” to understand the conversion.

I’m now trying to make python-code that convert MERL-data to
tensor tree data that can put in ScatteringData tags in xml.
Your advice will to be helpful.

Best, Takushi.