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node select by boundary
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Keep the items a closed loop encloses. Enclosed keeps only what is wholly inside; turn it off to keep what the loop touches as well.
Category: Data | Add menu: Data > Select by Boundary
Routes each item to Selected or Unselected by whether a closed loop encloses it. Wire the loop to Boundary and the things to test to Geometry. The loop has its own port, so it is never part of its own answer.
Enclosed is a switch on the node face and starts on, which is the strict reading: only what lies wholly inside is kept. Turn it off and anything the loop touches is kept too, so a shape straddling the edge comes out Selected rather than Unselected. Loosening the test is the deliberate move, not the default.
- Geometry (any): the items to test.
- Boundary (any): the closed loop, or loops, that do the enclosing.
- Enclosed (boolean, switch on the node face: default on): on keeps only what is wholly inside; off also keeps what the loop touches.
- Selected (any): the items the boundary encloses.
- Unselected (any): everything else.
Both outputs are live, so nothing is thrown away. Wire Unselected up as well to see what the loop is catching before you build on the answer.
Items, the same way Select by Area and Select Every Nth count them, so a region and its holes are tested and kept together rather than coming apart. An item resting exactly on the loop counts as inside.
A boundary does not have to be one ring. It can be several separate shapes, each tested on its own with the answers merged, so an item inside any one of them is selected. Two islands drawn apart from each other both select what they enclose.
Inside one shape the reading is even-odd: inside the outer ring and outside an inner one is in. A ring with a hole in it therefore behaves the way it looks, and something sitting in the hole is out.
A boundary it cannot use selects nothing: the whole input comes out on Unselected and the node raises the red attention badge. It does not pass the input through to Selected, which would read as a working test, and it does not close a gap for you, which would invent geometry you did not draw.
Hovering the badge gives the reason, one of three:
- Nothing is wired to Boundary.
- Boundary does not close: there is a gap between two ends.
- Boundary closes but encloses nothing.
- Select by Area: the same sorting by size rather than by position.
- Select Every Nth: by index, with the complement on the other output.
- Select by Condition: by a true or false you compute yourself.
- Data nodes: the rest of the category.
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