Swing Sight
A golf GPS you wore instead of held: 3D glasses that painted the pin, the carry number and the green's contour onto the fairway in front of you.
CREATED JAN 12, 2026 · UPDATED MAY 4, 2026
CAUSE OF DEATH
Four independent physical limits, any one of which was fatal on its own, all pointing at the same verdict: the job is to produce one number, and one number does not need three dimensions. Phone-class GNSS is accurate to three to five metres when the overlay needs sub-metre or the flag visibly floats off the green; magnetometer heading drifts ten to fifteen degrees beside a steel-framed cart and a golf bag, which at 150 yards is a forty-yard error in where the pin is drawn; a mown fairway is a low-texture plane, the worst possible input for the visual-inertial tracking that would otherwise correct both; and a sunlit fairway runs three to ten thousand nits against consumer waveguide optics that deliver one to two, so the overlay washed out in exactly the conditions golf is played in. The rules finished it: under the Rules of Golf a device that measures elevation change or recommends a club is a breach unless the feature is disabled, so the interesting half could not be used in any round that counted.
PROBLEM
A rangefinder answers 'how far to the pin' in about four seconds, but only if you have a clear line to the flag, you remember to bring it, and you are willing to stop walking, raise it, and steady your hands. A watch answers instantly and only tells you the middle of the green. Neither tells you what is between you and the pin.
HYPOTHESIS
If the distance, the carry over the bunker, and the slope of the green were painted onto the world in front of you, the information would stop being a lookup and become part of looking — no device raised, no interruption, and spatial facts delivered spatially.
ARCHITECTURE
iPhone as the compute and GNSS source, driving a tethered pair of birdbath-optic glasses. Position from CoreLocation fused with ARKit's visual-inertial odometry; hole geometry as a georeferenced spline per hole with green polygons and hazard boundaries, the same model shape that later survived into Stagger's course tables. Distances computed against the pin position for the day, not the green centre, which was the entire point — and also the piece with no data source that was not a licensing negotiation.
STACK
RESULT
Killed at the prototype stage after four months. Three test rounds settled it: the overlay was unreadable in direct sun, drifted off the green whenever the phone sat in the cart's steel frame, and the two seconds of re-localisation after every walk down the fairway cost more attention than raising a rangefinder ever did. The one surviving artifact is the course-geometry model — per-hole splines with green coordinates — which is why Stagger's hole table carries nullable green latitude and longitude columns to this day.
MEASURED
| metric | value | baseline |
|---|---|---|
| GNSS accuracy achieved | 3–5 m · phone-class single-frequency; RTK would need a base station per course | sub-metre needed to pin an overlay |
| heading error near a cart | 10–15° · magnetometer beside a steel frame and fourteen clubs | ≈1° needed at 150 yd |
| display brightness | 1–2k nits | 3–10k nits ambient on a sunlit fairway |
| battery under continuous use | ~2 h | 4.5 h round |
| test rounds before the call | 3 | — |
| information actually needed | 1 number · the finding that ended it | — |
LEARNINGS
- Rule out the physics before writing the app. Ambient brightness, GNSS accuracy and magnetometer drift are published numbers — an afternoon with them would have replaced four months of building.
- Augmented reality is worth its cost when the answer is a shape. When the answer is a scalar, a watch face beats a headset and always will.
- A low-texture surface is the adversarial case for visual-inertial tracking, and a mown fairway is the most low-texture surface in outdoor sport. The venue was the worst possible venue for the technique.
- Check the governing rules before the market, not after. Anything that measures slope or recommends a club is unusable in a counting round, which cut the addressable use to casual play only.
- Wearables have a social cost that does not appear in any spec. Four and a half hours of glasses over prescription sunglasses is a real objection and nobody was going to argue with it.
- The data model outlived the product. Georeferenced hole geometry was the genuinely hard part, it was correct, and it went straight into Stagger — a dead project can still be a component supplier.
PROVENANCE
Prototype built with Claude Code against a written spec; the autopsy below is the spec re-read after the third test round, with each assumption marked against what the hardware actually did.