How to emit particles from surfaces in normal direction?

I cannot use $NX, $NY, $NZ etc as initial velocities, the particles are supposed to carry attributes from the surface. :?:

you could multiply you Normal by your surface attribute.

ops: Im sorry i dont get it. Im getting “Unable to evaluate expression” while using $NX, $NY , $NZ in Velocity params.

Whats the most likely way to emit particles from surface in direction of normals in Houdini?

are you using POPs? if your emitter surface has normals on it (check and see), particles emitted on it using either points or surfaces as emission method (not volumes) will inherit the normals as initial velocity automatically. in the source POP go to the “attributes” tab and check if initial velocity is set to “use inherited velocity” and the value for inherit velocity is larger than 0.

cheers,
Abdelkareem

I created a sphere, polygon geometry.
Used “Source from Geometry” shelf tool.
And followed your steps. But particles just born and do not move at all.

you need to add a facet SOP to your sphere and compute normals. Particles use point Normals.

Great, it worked, actually i messed with Facet before but did not selected the proper node in Object Merge, so i was not seeing the end result.

Anyway, thanks every one