A molecular trajectory can be difficult to interpret when you only watch it move forward. A change may happen quickly, an intermediate conformation may be easy to miss, or you may want to revisit a structural transition without repeatedly scrubbing through the whole path. Playing a stored path in reverse offers a simple way to review the same sequence from its endpoint back to its starting frame.
Reverse playback is a viewing tool
In SAMSON, a path node stores a trajectory. The Play reverse path animation plays that path backwards between two animation keyframes. It can help you inspect how the structure returns through the conformations already present in the path, or make a presentation that starts with a later state and retraces the recorded sequence.
It is useful to keep one distinction in mind: reverse playback changes the order in which the stored path is displayed. It does not, by itself, calculate a new molecular trajectory or establish that the reverse sequence is a physically valid process. Treat it as a way to review and communicate the frames you have, not as a substitute for a simulation or analysis.
Set up the animation
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Choose the path you want to review. The path node is the object that stores the trajectory.
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In the Animator, open the Animation panel and double-click Play reverse path.
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Review the animation between its two keyframes. Move the keyframes as needed to adjust where the reverse playback begins and ends in the animation.
This workflow is especially handy when preparing a focused explanation: rather than replaying a long trajectory from the beginning, you can place the animation over the portion of the timeline you want to show. Keyframes can be moved later, so you can refine the timing as you build the presentation.
When multiple paths are selected
You can select more than one path before adding the animation. If multiple paths are selected, they are synchronized. This is useful when you want to view several paths together and have them play in reverse in step with one another. Before presenting the result, check that the paths you selected are the ones you intend to compare and that their playback is clear at the chosen animation timing.
Check smoothing and timing
The number of frames in the animation may not match the number of frames in the path. When they differ, the path is smoothed. Smoothing can affect how the motion appears between stored frames, so if you need to inspect or show the path without that smoothing, switch it off in the Inspector. This is worth checking when an in-between motion looks different from what you expected based on the path’s frames.
You can also change how parameters are interpolated between frames by modifying the animation’s easing curve. Easing affects the timing of interpolation, so it can help you adjust the presentation of the reverse playback. It does not change which path is being played. If the motion feels too fast or uneven for an explanation, check the animation timing and easing, as well as the smoothing setting.
A practical review checklist
- Confirm that the intended path or paths are selected.
- Use the keyframes to define the part of the animation where reverse playback should occur.
- If several paths are selected, remember that they will be synchronized.
- If the displayed motion seems unexpected, check whether the animation and path have different frame counts and whether smoothing is enabled.
- Adjust the easing curve if you want to change how interpolation is presented between frames.
Reverse playback is a small but useful option when a trajectory is easier to understand by retracing its recorded conformations. For the detailed instructions, see the Play reverse path documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.