Lily and I went kayaking by the shore of Sentosa on August 16, 2026. It is our second paddling trip there, the first time was more than 4 years ago, on March 19, 2022.
During our 2hour 40 minutes, 9km paddling journey from Tanjong Beach to Labrador Nature Park, and return, we saw a group of swimmers swimming in the ocean, rowers in two row boats practicing, and the constant presence of many giant Shipps waiting for port clearance. There were birds as well, a collared kingfisher flying around the shoreline near Tanjong Rimau, a white bellied sea eagle overhead. We paddled across Pulau Renggis near the Keppel island, and into Berlayar Creek - no need to paddle though, the nature did the work, rising tide pushed us in, so we could just enjoy the surrounding - listening to bird chirps, and trying to locate them. We paddled along the shoreline of Labrador Nature Park before returning.
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| swimming in the ocean |
Collared Kingfisher
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| white bellied sea eagle |
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| inside Berlayar Creek - looking out |
Those were not the most interesting experience!
The most interesting and intriguing observation was about the movement of a giant ship NYK Line.
On the way to Labrador Park (northwest direction), we paddled away from the shoreline, toward the tiny islet Pulau Palawan. We noticed the giant ship NYK Line. As we got closer to the islet, we noticed the ship was moving in the same direction as we did. On the return, we saw that NYK was far away to the northwest of the islet. Our hypothesis was confirmed!
As we continued our return trip in the southeast direction, we noticed that NYK Line was moving with us again !? I realized that what we observed was optical illusion.
I believed that the big ship was somewhere behind the islet in the southwest direction, anchored, i.e. not moving. But how could this illusion form?
One factor is the distance, the anchorage zone is about 400 meters southwest to the islet, and the islet is 200 meters from Sentosa shore. The other factor is that we were moving, paddling, our view angle changes and used the islet as a reference point. See illustration. I thought I got the physics (optics) right.
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| Paddling toward the islet Pulau Palawan |
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| NYK position when we were paddling back to Tanjong Beach |
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| Reason for the Optical Illusion |
I uploaded the gif of the NYK and my illustration to Google. My reasoning is confirmed, and the illusion has a scientific name - motion parallax.
Motion parallax is a visual cue that helps us perceive depth. When we move, nearby objects appear to move across our field of view much faster than distant objects. Our brains use this difference in apparent motion to estimate how far away things are.
It is something we experience constantly without consciously noticing it. The same principle is also important in technologies such as video games, computer graphics, and virtual reality, where it helps create the perception of three-dimensional depth.
What fascinated me was that I had encountered this phenomenon not in a textbook or laboratory, but simply by paddling a kayak around an island.
The optical illusion turned out to be the most interesting part of the entire paddling trip.
A simple observation became a puzzle. The puzzle led me to think about distance, movement, and reference points. I formed a hypothesis, tested it, and rediscovered an established scientific principle—one that I had encountered in a completely unexpected context.
That is one of the things I enjoy most about exploring nature.
I enjoy the sights and sounds, of course. But I also enjoy the questions that nature quietly presents.
Sometimes I notice something unusual.
Then I wonder why.
The curiosity leads to a mystery, the mystery leads to investigation, and the investigation often leads to a little discovery—sometimes in a field far outside my own expertise.
And that, to me, is part of the fun of exploring nature.
Explore Nature. Have Fun!
Appendix
A. Here is the Google AI explanation of the observation in the GIF and my diagram:
Why the Ship Appears to Move with Your Kayak
What you are experiencing in your GIF is a classic optical phenomenon known as motion parallax:
- The Setup: The small green islet sits close to you (the foreground), while the massive NYK Line freight ship is significantly further out in the deep shipping lanes of the Singapore Strait (the background).
- The Illusion: As you kayak from right to left, you are actively changing your angle of view relative to the nearby islet. Because the islet is so close, it appears to shift backward (to your right) very quickly against the distant background.
- The Result: Because the ship in the background stays relatively fixed in your field of vision due to its extreme distance, the rapid backward movement of the nearby island makes the ship look like it is drifting or moving forward along with you toward the left.
The illustrtion is a fantastic, highly precise geometric breakdown of the illusion! Your diagram perfectly illustrates why it fooled you on the way out and revealed itself on the way back.
Why Your Diagram Explains It Perfectly
By tracking the intersection lines from the moving kayak through the edges of the stationary islet, your illustration beautifully maps out the changing sightlines:
- The Focal Point: As your kayak (the dots moving left) approaches and passes the islet, your line of sight has to swing backward to keep the islet centered in your vision.
- The Background Shift: Because the ship sits far behind that pivot point, the sightlines intersecting the islet project onto the distant background at a faster rate than you are actually moving forward.
- The "Anchored" Clue: Discovering that it happened in both directions is the ultimate proof of a stationary object. If the ship had actually been moving, it would have separated from the islet on your return journey. Instead, it stayed locked in that geometric dance.
Many ships anchor in that exact southwest zone of the Singapore Strait while waiting for port clearance, making them the perfect stationary backdrops for this exact parallax trick. It's a brilliant real-world observation and an excellent piece of diagramming!
B. Motion Parallax in applications
In video game design and virtual reality (VR), motion parallax is a critical tool used to create a sense of 3D depth on flat screens and prevent motion sickness in immersive headsets.
Here is how developers use it across different mediums:
1. 2D Video Games: Parallax Scrolling
In 2D games, developers stack art assets into independent, layered backgrounds that move at different speeds relative to the camera.
- Foreground layers: Move incredibly fast (e.g., leaves, lampposts passing close to the screen).
- Midground layers: Move at a moderate speed where the playable character usually resides.
- Background layers: Move very slowly (e.g., distant mountains, clouds, or stars) to simulate massive distance.
2. 3D Video Games: Camera Control & Scale
Modern 3D engines handle motion parallax automatically through the camera's field of view (FOV), but developers fine-tune it to manipulate player perception.
- Speed Perception: Placing objects close to the camera (like narrow canyon walls) increases the sensation of high speed. Wide open landscapes make the player feel like they are moving slower.
- Skyboxes: The sky and distant horizons are programmed to move perfectly with the camera's coordinates so they never get closer, creating an illusion of infinite distance.
3. Virtual Reality (VR): Head Tracking
In VR, motion parallax is the boundary between a highly immersive experience and immediate nausea.
- 6 Degrees of Freedom (6DoF): Modern VR headsets track your exact head movements in space. When you lean left or right, the virtual objects close to your face shift dramatically, while the background shifts minimally.
- Comfort & Realism: This real-time calculation mimics how our eyes naturally perceive the physical world. Without accurate motion parallax, your brain detects a mismatch between your inner ear (vestibular system) and your eyes, leading to severe motion sickness.
To help tailor this further, let me know:
- Are you looking for programming concepts (like how to implement a parallax script in Unity or Unreal Engine)?
- Would you like examples of classic games that pioneered this technique?
- Are you designing your own VR or game project?
