diff --git a/src/geometry/shape.rs b/src/geometry/shape.rs
index 671b471..cf68147 100644
--- a/src/geometry/shape.rs
+++ b/src/geometry/shape.rs
@@ -13,6 +13,18 @@ pub trait ShapeTrait {
     fn envelope(&self, margin: f64) -> AABB<[f64; 2]>;
     fn width(&self) -> f64;
     fn length(&self) -> f64;
+
+    fn flat_envelope_3d(&self, margin: f64, layer_count: u64) -> AABB<[f64; 3]> {
+        let envelope = self.envelope(margin);
+        AABB::from_corners(
+            [envelope.lower()[0], envelope.lower()[1], 0.0],
+            [
+                envelope.upper()[0],
+                envelope.upper()[1],
+                (layer_count - 1) as f64,
+            ],
+        )
+    }
 }
 
 #[enum_dispatch(ShapeTrait)]
diff --git a/src/geometry/with_rtree.rs b/src/geometry/with_rtree.rs
index 6333eae..c901b47 100644
--- a/src/geometry/with_rtree.rs
+++ b/src/geometry/with_rtree.rs
@@ -7,7 +7,7 @@ use rstar::{primitives::GeomWithData, RTree, RTreeObject};
 
 use crate::{
     graph::{GenericIndex, GetNodeIndex},
-    layout::graph::Retag,
+    layout::graph::{GetLayer, Retag},
 };
 
 use super::{
@@ -19,10 +19,10 @@ type BboxedShapeAndIndex<GI> = GeomWithData<Shape, GI>;
 
 #[derive(Debug)]
 pub struct GeometryWithRtree<
-    GW: GetWidth + TryInto<DW> + TryInto<SW> + TryInto<BW> + Retag<GI> + Copy,
-    DW: DotWeightTrait<GW> + Copy,
-    SW: SegWeightTrait<GW> + Copy,
-    BW: BendWeightTrait<GW> + Copy,
+    GW: GetWidth + GetLayer + TryInto<DW> + TryInto<SW> + TryInto<BW> + Retag<GI> + Copy,
+    DW: DotWeightTrait<GW> + GetLayer + Copy,
+    SW: SegWeightTrait<GW> + GetLayer + Copy,
+    BW: BendWeightTrait<GW> + GetLayer + Copy,
     GI: GetNodeIndex + TryInto<DI> + TryInto<SI> + TryInto<BI> + Copy,
     DI: GetNodeIndex + Into<GI> + Copy,
     SI: GetNodeIndex + Into<GI> + Copy,
@@ -30,6 +30,7 @@ pub struct GeometryWithRtree<
 > {
     geometry: Geometry<GW, DW, SW, BW, GI, DI, SI, BI>,
     rtree: RTree<BboxedShapeAndIndex<GI>>,
+    layer_count: u64,
     weight_marker: PhantomData<GW>,
     dot_weight_marker: PhantomData<DW>,
     seg_weight_marker: PhantomData<SW>,
@@ -43,20 +44,21 @@ pub struct GeometryWithRtree<
 #[debug_invariant(self.test_envelopes())]
 #[debug_invariant(self.geometry.graph().node_count() == self.rtree.size())]
 impl<
-        GW: GetWidth + TryInto<DW> + TryInto<SW> + TryInto<BW> + Retag<GI> + Copy,
-        DW: DotWeightTrait<GW> + Copy,
-        SW: SegWeightTrait<GW> + Copy,
-        BW: BendWeightTrait<GW> + Copy,
+        GW: GetWidth + GetLayer + TryInto<DW> + TryInto<SW> + TryInto<BW> + Retag<GI> + Copy,
+        DW: DotWeightTrait<GW> + GetLayer + Copy,
+        SW: SegWeightTrait<GW> + GetLayer + Copy,
+        BW: BendWeightTrait<GW> + GetLayer + Copy,
         GI: GetNodeIndex + TryInto<DI> + TryInto<SI> + TryInto<BI> + PartialEq + Copy,
         DI: GetNodeIndex + Into<GI> + Copy,
         SI: GetNodeIndex + Into<GI> + Copy,
         BI: GetNodeIndex + Into<GI> + Copy,
     > GeometryWithRtree<GW, DW, SW, BW, GI, DI, SI, BI>
 {
-    pub fn new() -> Self {
+    pub fn new(layer_count: u64) -> Self {
         Self {
             geometry: Geometry::<GW, DW, SW, BW, GI, DI, SI, BI>::new(),
             rtree: RTree::new(),
+            layer_count,
             weight_marker: PhantomData,
             dot_weight_marker: PhantomData,
             seg_weight_marker: PhantomData,
@@ -206,10 +208,10 @@ impl<
 }
 
 impl<
-        GW: GetWidth + TryInto<DW> + TryInto<SW> + TryInto<BW> + Retag<GI> + Copy,
-        DW: DotWeightTrait<GW> + Copy,
-        SW: SegWeightTrait<GW> + Copy,
-        BW: BendWeightTrait<GW> + Copy,
+        GW: GetWidth + GetLayer + TryInto<DW> + TryInto<SW> + TryInto<BW> + Retag<GI> + Copy,
+        DW: DotWeightTrait<GW> + GetLayer + Copy,
+        SW: SegWeightTrait<GW> + GetLayer + Copy,
+        BW: BendWeightTrait<GW> + GetLayer + Copy,
         GI: GetNodeIndex + TryInto<DI> + TryInto<SI> + TryInto<BI> + PartialEq + Copy,
         DI: GetNodeIndex + Into<GI> + Copy,
         SI: GetNodeIndex + Into<GI> + Copy,
diff --git a/src/layout/layout.rs b/src/layout/layout.rs
index 2f837c3..904c2d7 100644
--- a/src/layout/layout.rs
+++ b/src/layout/layout.rs
@@ -82,7 +82,7 @@ pub struct Layout<R: RulesTrait> {
 impl<R: RulesTrait> Layout<R> {
     pub fn new(rules: R) -> Self {
         Self {
-            geometry_with_rtree: GeometryWithRtree::new(),
+            geometry_with_rtree: GeometryWithRtree::new(2),
             rules,
         }
     }