Add oGetRelativeFrame method to LocalFrame

ShapeKernel/Frames/LocalFrame.cs

@@ -202,6 +202,31 @@ public static LocalFrame oGetRotatedFrame(LocalFrame oFrame, float dPhi, Vector3
                 return oNewFrame;
             }
 
+	    /// <summary>
+	    /// Returns a new LocalFrame positioned at an offset relative to the given reference frame. 
+            /// The offset is interpreted in the reference frame's local coordinate system.
+	    /// Use caution if chaining relative frames as inaccuracies can compound. 
+	    /// </summary>
+	    /// <param name="refFrame">The LocalFrame whose local axes define the translation directions</param>
+	    /// <param name="vecLocalOffset">Translation vector in the reference frame's local coordinates</param> 
+	    /// <returns>A new LocalFrame translated relative to the reference frame</returns>
+	    public static LocalFrame oGetRelativeFrame(LocalFrame refFrame, Vector3 vecLocalOffset)
+	    {
+		Vector3 vecRefX = refFrame.vecGetLocalX();
+		Vector3 vecRefY = refFrame.vecGetLocalY();
+		Vector3 vecRefZ = refFrame.vecGetLocalZ();
+
+		Vector3 vecGlobalOffset =
+		vecRefX * vecLocalOffset.X 
+		vecRefY * vecLocalOffset.Y +
+		vecRefZ * vecLocalOffset.Z;
+
+		Vector3 vecNewPosition = refFrame.vecGetPosition() + vecGlobalOffset;
+
+		return new LocalFrame(vecNewPosition, refFrame.vecGetLocalZ(), refFrame.vecGetLocalX());
+	    }
+
+
             /// <summary>
             /// Compliments local z and local x according to a right-hand system.
             /// </summary>
@@ -212,4 +237,4 @@ public static Vector3 vecGetLocalY(Vector3 vecLocalZ, Vector3 vecLocalX)
             }
         }
     }
-}
+}