Hi @angelo.figliola and @chris,
For getting XML files that were generated from empirically measured data using a photogoniometerat LBNL, use the Window 7.4 database. That has 1000s of XML files. The process for generating them is covered in the Three Phase Tutorial (see section 3.2.1). The instruction manual for Window 7.4 also discusses the process for generating XMLs by combining multiple XML files (for example, combining the XMLs for a glazing and venetian blinds).
One of our HB repositories has several XMLs that were downloaded from the Building Components Library database.
You can also make your own XML files using the Radiance genBSDF program. This tutorial explains how.
Finally, a very quick (albeit hacky) way to check if an XML is specular or not is to visualize it’s matrix as an hdr. Specular XMLs usually have a clear diagonal line across them while diffused ones show scattered patterns. Something which is both specular and diffusing will produce an intermediate pattern. Here are a few examples:
The xml files for the above image:xmls.zip (521.8 KB)
The command for generating those files will be something like:
rmtxop -fc clear.xml|pfilt -x 300 -y 300 |ra_tiff - clear.tiff