diff --git a/Photorealistic-Rendering-Engine-based-on-Unreal-Engine.md b/Photorealistic-Rendering-Engine-based-on-Unreal-Engine.md
index ffcea0b..d43204f 100644
--- a/Photorealistic-Rendering-Engine-based-on-Unreal-Engine.md
+++ b/Photorealistic-Rendering-Engine-based-on-Unreal-Engine.md
@@ -25,4 +25,6 @@ To visualize the output of the simulator, you can open `rviz` (from a new termin
 You can also open `rqt` for more visualizations, as follows:
 
     roscd esim_visualization
-    rqt --perspective-file cfg/esim.perspective
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+    rqt --perspective-file cfg/esim.perspective
+
+Note that this rendering engine is very slow: rendering a one minute trajectory may take multiple hours.
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