How to get a tangent vector for a vertex in VTK9.0?

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1

Hi,
I want to use a MERL material on a polydata, but I’m confused about how to get a tangent vector for a vertex in vertex shader.
Thanks!

2

I found vtkPolyDataTangents in VTK, but an error occurred “Texture coordinates are requested to generate tangents.”, is there any way to get the tangent without providing Tcoords?