diff --git a/frontend/js/labs/stereo.js b/frontend/js/labs/stereo.js
index 20d9585..b495f0d 100644
--- a/frontend/js/labs/stereo.js
+++ b/frontend/js/labs/stereo.js
@@ -769,7 +769,7 @@ class StereoSim {
     topRing.position.y = h;
     this._figGroup.add(topRing);
 
-    // edges: two vertical lines + center
+    // edges: vertical generators + center axis
     const n = 8;
     for (let i = 0; i < n; i++) {
       const angle = (i / n) * Math.PI * 2;
@@ -780,6 +780,13 @@ class StereoSim {
     this._vertices.push({ pos: new THREE.Vector3(0, 0, 0), label: 'O₁' });
     this._vertices.push({ pos: new THREE.Vector3(0, h, 0), label: 'O₂' });
     this._edges.push({ from: new THREE.Vector3(0, 0, 0), to: new THREE.Vector3(0, h, 0) });
+    // base/top circle arc segments (for point-picking)
+    const arcN = 32;
+    for (let i = 0; i < arcN; i++) {
+      const a1 = (i / arcN) * Math.PI * 2, a2 = ((i + 1) / arcN) * Math.PI * 2;
+      this._edges.push({ from: new THREE.Vector3(r * Math.cos(a1), 0, r * Math.sin(a1)), to: new THREE.Vector3(r * Math.cos(a2), 0, r * Math.sin(a2)) });
+      this._edges.push({ from: new THREE.Vector3(r * Math.cos(a1), h, r * Math.sin(a1)), to: new THREE.Vector3(r * Math.cos(a2), h, r * Math.sin(a2)) });
+    }
 
     this._addEdges(0.4);
     this._addVerticesAndLabels();
@@ -814,6 +821,15 @@ class StereoSim {
       this._edges.push({ from: new THREE.Vector3(x, 0, z), to: apex });
     }
     this._edges.push({ from: new THREE.Vector3(0, 0, 0), to: apex });
+    // base circle as arc segments (for point-picking)
+    const arcN = 32;
+    for (let i = 0; i < arcN; i++) {
+      const a1 = (i / arcN) * Math.PI * 2, a2 = ((i + 1) / arcN) * Math.PI * 2;
+      this._edges.push({
+        from: new THREE.Vector3(r * Math.cos(a1), 0, r * Math.sin(a1)),
+        to:   new THREE.Vector3(r * Math.cos(a2), 0, r * Math.sin(a2)),
+      });
+    }
 
     this._addEdges(0.4);
     this._addVerticesAndLabels();
@@ -851,6 +867,13 @@ class StereoSim {
         to:   new THREE.Vector3(r * Math.cos(angle), h, r * Math.sin(angle)),
       });
     }
+    // circle arc segments for point-picking on both bases
+    const arcN = 32;
+    for (let i = 0; i < arcN; i++) {
+      const a1 = (i / arcN) * Math.PI * 2, a2 = ((i + 1) / arcN) * Math.PI * 2;
+      this._edges.push({ from: new THREE.Vector3(R * Math.cos(a1), 0, R * Math.sin(a1)), to: new THREE.Vector3(R * Math.cos(a2), 0, R * Math.sin(a2)) });
+      this._edges.push({ from: new THREE.Vector3(r * Math.cos(a1), h, r * Math.sin(a1)), to: new THREE.Vector3(r * Math.cos(a2), h, r * Math.sin(a2)) });
+    }
 
     this._addEdges(0.4);
     this._addVerticesAndLabels();