inquiring for the "vc" keyword found in .obj file

[jimmy-academia]

In the example .obj file provided in https://deep-geometry.github.io/abc-dataset/, there are multiple lines starting with 'vc', e.g.

vc 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 -1.000000
vc 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 -1.000000
vc 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 0.000000 -1.000000

I could not find any description of the keyword "vc" regarding .obj file formats. (For examples, I checked Wavefront OBJ File Format Summary, Alias/WaveFront Object (.obj) File Format)

I am curious to know what the "vc" keyword describes.
Thank you!

[ivanpuhachov]

I'm assuming "vc" stands for "vertex curvature" as in file descriptions.
However, I haven't found any specifications on the format, so I'm guessing here:

vc -103.586413 -0.000000 0.058779 -0.998271 0.000000 -0.705884 -0.041563 0.707107

means that the surface principal curvatures at this vertex are -103.586413 and 0.000000, and the corresponding principal directions are (-0.000000 0.058779 -0.998271) and (-0.705884 -0.041563 0.707107) - notice that these vectors are normalized to 1.

But a clarification from the authors is still required.