diff --git a/src/bin/flat/tube/mod.rs b/src/bin/flat/tube/mod.rs
index eefa4b3..70b85cb 100644
--- a/src/bin/flat/tube/mod.rs
+++ b/src/bin/flat/tube/mod.rs
@@ -4,6 +4,7 @@ use crate::riemann::Metric;
 use Subspace::{Boundary, Inner, Outer};
 use metric::Tube;
 use coords::{FlatCoordinateSystem, InnerCS, OuterCS};
+use crate::tube::coords::FlatRegion;
 use crate::types::{FlatTraceResult, Hit, Location, Object, Ray};
 
 pub mod metric;
@@ -56,23 +57,17 @@ impl Space {
 
 	pub fn trace_inner(&self, ray: Ray) -> FlatTraceResult {
 		assert_eq!(self.which_subspace(ray.pos), Inner);
-		let cs = InnerCS(self.tube);
-		let inner = Rect { size: vec2(self.tube.inner_radius, self.tube.internal_halflength) };
-		let ray = cs.global_to_flat(ray);
-		assert!(inner.is_inside(ray.pos));
-		let dist = inner.trace_out_of(ray);
-		self.trace_flat(cs, ray, dist)
+		self.trace_flat(InnerCS(self.tube), ray)
 	}
 
 	pub fn trace_outer(&self, ray: Ray) -> FlatTraceResult {
 		assert_eq!(self.which_subspace(ray.pos), Outer);
-		let cs = OuterCS(self.tube);
-		let outer = Rect { size: vec2(self.tube.outer_radius, self.tube.external_halflength) };
-		let dist = outer.trace_into(ray);
-		self.trace_flat(cs, ray, dist)
+		self.trace_flat(OuterCS(self.tube), ray)
 	}
 
-	fn trace_flat(&self, cs: impl FlatCoordinateSystem<Vec2> + FlatCoordinateSystem<Ray> + FlatCoordinateSystem<Location>, ray: Ray, dist: Option<f32>) -> FlatTraceResult {
+	fn trace_flat(&self, cs: impl FlatRegion, ray: Ray) -> FlatTraceResult {
+		let ray = cs.global_to_flat(ray);
+		let dist = cs.distance_to_boundary(ray);
 		let objs = self.list_objects(|loc| cs.global_to_flat(loc));
 		FlatTraceResult {
 			end: dist.map(|dist| cs.flat_to_global(ray.forward(dist))),
@@ -200,6 +195,11 @@ mod coords {
 		fn global_to_flat(&self, v: T) -> T { v }
 	}
 
+	pub trait FlatRegion: FlatCoordinateSystem<Vec2> + FlatCoordinateSystem<Ray> + FlatCoordinateSystem<Location> {
+		// Измеряет расстояние до выхода за пределы области вдоль луча ray. Луч задаётся в плоской СК.
+		fn distance_to_boundary(&self, _ray: Ray) -> Option<f32> { None }
+	}
+
 	pub struct InnerCS(pub Tube);
 
 	impl FlatCoordinateSystem<Vec2> for InnerCS {
@@ -241,6 +241,12 @@ mod coords {
 		}
 	}
 
+	impl FlatRegion for InnerCS {
+		fn distance_to_boundary(&self, ray: Ray) -> Option<f32> {
+			Rect { size: vec2(self.0.inner_radius, self.0.internal_halflength) }.trace_out_of(ray)
+		}
+	}
+
 	pub struct OuterCS(pub Tube);
 
 	impl FlatCoordinateSystem<Vec2> for OuterCS {}
@@ -268,6 +274,12 @@ mod coords {
 		}
 	}
 
+	impl FlatRegion for OuterCS {
+		fn distance_to_boundary(&self, ray: Ray) -> Option<f32> {
+			Rect { size: vec2(self.0.outer_radius, self.0.external_halflength) }.trace_into(ray)
+		}
+	}
+
 	#[cfg(test)]
 	mod test {
 		use super::{Location, Tube, OuterCS, FlatCoordinateSystem};