Hi, i have a model with many primitives. Their respective normals are all pointing towards different direction. How do i orientate all of them in a single direction, eg, all in the upward direction?

in the facet SOP, check “Orient Polygons” 8)

Primitive normals are driven from the primitive faces and the vertex winding order. The primitive face determines the primitive orientation and the vertex winding order determines the normal direction.

The only way to modify the primitive normal is to either reverse the vertex order or transform the primitive.

You can reverse the vertex order to flip the primitive normal with the Vertex SOP, Primitive SOP or the Ends SOP. Starlkerx777's answer with the Orient Polygons is a good one when adjacent primitives have flipped primitive normal directions as this can wreak havoc with smooth shading of rendered surfaces as point/vertex shading normals are constructed from the primitive normal direction.

Primitive normals are driven from the primitive faces and the vertex winding order. The primitive face determines the primitive orientation and the vertex winding order determines the normal direction.

The only way to modify the primitive normal is to either reverse the vertex order or transform the primitive.

You can reverse the vertex order to flip the primitive normal with the Vertex SOP, Primitive SOP or the Ends SOP. Starlkerx777's answer with the Orient Polygons is a good one when adjacent primitives have flipped primitive normal directions as this can wreak havoc with smooth shading of rendered surfaces as point/vertex shading normals are constructed from the primitive normal direction.