I really new in Houdini, i want to set pivot at center a group of primitives and
transform it.

If you want to transform them individually, you can use the Primitive SOP.

moder
I really new in Houdini, i want to set pivot at center a group of primitives and
transform it.

EditSOP does it by default, it moves the pivot accordingly to input group. As to TransformSOP, there is a local variable $GCX/Y/Z, you can put into Pivot parameter for the same effect.

hth,
skk.

SYmek..I try $GCY and it is what it want, thank you all.

Does anyone know if there's an easy way to rotate a primitive about it's normal?

Do you guys know if the $GCX-Y-Z uses the area of the faces?
I'm having a hard time trying to redo a script from max with SOPs.

Example:
- Geometry with a fuse SOP to make each point unique.
- Apply a primitive SOP to do a transformation and scale to zero. This will give a clump of points at the center of each primitive.
- Do assemble SOP, forEach loop then apply a transform SOP of the same previous geometry, transform SOP allows for using both $CEX or $GCX expressions pivots. Scale to zero. The outcome is not the same as the previous case.

The reason for using the area is because points shared between big triangles should contribute more to the average position compared to lots of tiny triangles.