diff --git a/src/PathPlanning/RailGeometryHelper.cs b/src/PathPlanning/RailGeometryHelper.cs
index 2eab161..3c9eb22 100644
--- a/src/PathPlanning/RailGeometryHelper.cs
+++ b/src/PathPlanning/RailGeometryHelper.cs
@@ -498,26 +498,28 @@ namespace NavisworksTransport.PathPlanning
                 var center = obb.Center;
                 var direction = principalAxis.ToVector3D();
                 
-                // 找到最接近"向下"方向的轴（Z 轴负方向）
-                var downAxisIndex = 1; // 默认使用 Axis 1（次长轴）
-                var minZComponent = 1.0; // Z 分量的最小值
+                // 找到 Z 轴方向的轴（使用点积绝对值最大法）
+                var zAxisDirection = new Vector3D(0, 0, 1); // Z 轴向上方向
                 
-                for (int i = 1; i < 3; i++) // 检查 Axis 1 和 Axis 2
+                // 计算所有轴与 Z 轴方向的点积绝对值
+                var absDotProducts = new double[2];
+                for (int i = 1; i < 3; i++)
                 {
                     var axis = obb.GetAxis(i);
                     var axisVector = axis.ToVector3D();
-                    var zComponent = axisVector.Z;
                     
-                    LogManager.Info($"[空轨] Axis {i} Z分量: {zComponent:F3}");
+                    // 计算点积：axis · zAxisDirection
+                    var dotProduct = axisVector.X * zAxisDirection.X + 
+                                         axisVector.Y * zAxisDirection.Y + 
+                                         axisVector.Z * zAxisDirection.Z;
+                    absDotProducts[i - 1] = Math.Abs(dotProduct);
                     
-                    // 找到 Z 分量最小的轴（最向下，即最负）
-                    if (zComponent < minZComponent)
-                    {
-                        minZComponent = zComponent;
-                        downAxisIndex = i;
-                    }
+                    LogManager.Info($"[空轨] Axis {i} 与 Z 轴方向点积: {dotProduct:F3}, 绝对值: {absDotProducts[i - 1]:F3}");
                 }
                 
+                // 选择点积绝对值最大的轴（最接近 Z 轴方向）
+                int downAxisIndex = absDotProducts[1] > absDotProducts[0] ? 2 : 1;
+                
                 var downAxis = obb.GetAxis(downAxisIndex);
                 var downAxisVector = downAxis.ToVector3D();
                 
@@ -771,9 +773,11 @@ namespace NavisworksTransport.PathPlanning
             }
 
             // 归一化方向
-            direction.X /= length;
-            direction.Y /= length;
-            direction.Z /= length;
+            direction = new Vector3D(
+                direction.X / length,
+                direction.Y / length,
+                direction.Z / length
+            );
 
             // 计算采样点数
             int numPoints = (int)Math.Ceiling(length / interval) + 1;
diff --git a/src/PathPlanning/SlopeAnalyzer.cs b/src/PathPlanning/SlopeAnalyzer.cs
index d041a13..afd9454 100644
--- a/src/PathPlanning/SlopeAnalyzer.cs
+++ b/src/PathPlanning/SlopeAnalyzer.cs
@@ -522,25 +522,4 @@ namespace NavisworksTransport.PathPlanning
         Other
     }
 
-    /// <summary>
-    /// 3D向量结构
-    /// </summary>
-    public struct Vector3D
-    {
-        public double X { get; set; }
-        public double Y { get; set; }
-        public double Z { get; set; }
-
-        public Vector3D(double x, double y, double z)
-        {
-            X = x;
-            Y = y;
-            Z = z;
-        }
-
-        public override string ToString()
-        {
-            return $"({X:F3}, {Y:F3}, {Z:F3})";
-        }
-    }
-}
\ No newline at end of file
+    }
\ No newline at end of file