Add access to velocity for LineTransformation

src/geometry/LineTransformation.hpp

@@ -59,6 +59,13 @@ class LineTransformation
     return x[0] * m_velocity + m_shift;
   }
 
+  PUGS_INLINE
+  const TinyVector<Dimension>&
+  velocity() const
+  {
+    return m_velocity;
+  }
+
   double
   velocityNorm() const
   {