Here’s a simple ICE tree that emits strands from a polygon cluster.
A general technique for these kinds of filtered emissions is to delete the points you don’t want. In this case, we check Cluster.IsElement. The tricky part is that Cluster.IsElement is a bool-per-polygon attribute, so we need to get into a per-point context. To do that, we get the emit location, which is per-point, and then at that location, the value of Cluster.IsElement. Now we’re in a per-point context, and we can use those per-point boolean values to delete points.
Note the use of Not instead of an If. We know IsElement is False for points that were not emitted from the polygon cluster, so we can logically negate it with Not to get True and feed that into Delete Point.
In pseudocode, we do this:
if not( IsElement ) delete point
if (IsElement == False) then delete point
Of course, for filtering we could just drill down into Emit Strands and set the filter on the Generate Sample Set nodes.