diff --git a/include/line.hpp b/include/line.hpp
index 29aa4f8..4b9b7a6 100644
--- a/include/line.hpp
+++ b/include/line.hpp
@@ -289,6 +289,8 @@ public:
         real h = std::clamp(AP.dot(AB) / AB.dot(AB), 0., 1.);
         return {h, (AP - AB * h).norm()};
     }
+
+    bool isEndParm(real t) { return t < EPS || t > _points.size() - 1 - EPS; }
 };
 
 class HelixLine : public ILine {
@@ -307,6 +309,10 @@ private:
     real startTheta; // 轴线起始时在螺旋投影（圆）上的参数
 };
 
+class SingleLine : public ILine {
+public:
+};
+
 class PolynomialLine : public ILine {
 public:
     Vec3 eval(real param) override { return {}; };
diff --git a/include/solid.hpp b/include/solid.hpp
index 701f1cf..f870310 100644
--- a/include/solid.hpp
+++ b/include/solid.hpp
@@ -19,11 +19,9 @@ inline Vec2 get2DRepOf3DPt(const Vec3 &pt3D, const Vec3 &u, const Vec3 &v, const
     Vec3 OP = pt3D - localO;
     return {OP.dot(u), OP.dot(v)};
 }
-
 inline Vec2 get2DRepOf3DDir(const Vec3 &dir, const Vec3 &u, const Vec3 &v) {
     return Vec2{dir.dot(u), dir.dot(v)}.normalize();
 }
-
 class IExtrudedSolid : public ISolid {
 public:
     std::vector<Polyline> _profiles; // TODO: may be replaced by const ref to profile
@@ -51,7 +49,6 @@ private:
     std::vector<std::vector<CircularArc<Vec2>>> _localArcs2d;
     // Pt2Array _localCircleCenter2D;
     // Pt2Array _localInCircleDir;
-
 public:
     ExtrudedSolidPolyline(std::vector<Polyline> profiles, Polyline axis, real rScale)
         : IExtrudedSolid(std::move(profiles), rScale), _axis(std::move(axis)) {
@@ -90,11 +87,17 @@ public:
         ClosestDescOnSeg closestDescToAxis = _axis.getClosestParam(p);
         // TNB coordinate system
         auto t = closestDescToAxis.t;
+        Vec3 Q = _axis.eval(t); // closest point on axis
+        Vec3 QP = p - Q;
         Vec3 T = _axis.der1(t).normalize();
+        if (_axis.isEndParm(t) && fabs(QP.dot(T)) > EPS) {
+            // project p to the plane passing through Q and perpendicular to T
+            Vec3 projP = p + T * (-QP.dot(T));
+        }
+
         Vec3 N = _axis.der2(t).normalize();
         Vec3 B = T.cross(N);
-        Vec3 Q = _axis.eval(t);
-        Vec3 QP = p - Q;
+
         auto p2D = get2DRepOf3DPt(QP, N, B, Q);
         // PMC
         PtBoundaryRelation ptProfileRelation = Inside;
@@ -109,6 +112,7 @@ public:
                 break;
             }
         }
+
         // distance
         ClosestDescOnSeg closestDescToProfile{};
         for (int i = 0; i < _localArcs2d.size(); ++i) {
@@ -122,7 +126,7 @@ public:
     }
 
 private:
-    /**
+    /** 低于2Dprofile的内外部判定
      * in + in = out
      * in + out = in
      * out + in = in