Implementation · 20.0 m

How we know it is 20.0 m

A 2% error on this court is 40 cm — enough to turn a legal touch into a miss, or the reverse. The method that draws the pretty overlay is not automatically the method that certifies the metre. This page tracks pending designs for the pathways worth building, and attempts so far against those pathways.

Product law stays fixed: tape or laser owns the official metre. AR, IMU, and camera assists may walk and draw. GPS never counts. Unsupervised depth reads of a parked phone are not a 20 m tape.

Pending design — pathways worth building

From the measure table on the notes: only the high design-fit / official-metre-pass methods. The shit ones (phone GPS, L1/L5 GNSS indoors, parked LiDAR as course length) are ignored here on purpose.

Pending design

Walk + steel tape (preferred)

Design fit ●●●●● · Official metre: pass

Phone walks the court (ARKit / ARCore VIO), drops two end anchors, then a steel tape or laser disto between the same marks becomes the certified length. AR only has to stay registered to those marks.

Why it matters Best setup UX with an honest metre. Scale error in wild VIO is commonly single-digit percent — fine for drawing, fatal as the official number without tape.
Pending design

Steel tape / laser only

Design fit ●●●●○ · Official metre: pass

Type the certified metres from a Class II tape (±mm over 20 m) or a laser disto (±1–3 mm). No camera model required for the metre itself. Human-judged nights can live here entirely.

Why it matters Perfect metre, zero VIO drama. The app still needs this field even when fancy walk-assist exists.
Pending design

Two phones on taped lines (Path C)

Design fit ●●●●● · Official metre: pass

Tape owns distance. One phone sits on each line so feet are close in frame. New risk is clock sync, not metres — one audio master, others slave to the beep.

Why it matters Far-line px/cm kills single wide cameras. Dual phones fix geometry; they invent misses without one clock.
Pending design

Laser disto / survey wheel certify step

Design fit ●●●●○ · Official metre: pass

Faster certify than a floppy 20 m tape. Same product rule: the reading is typed (or later captured) as the official length; the phone assist is not.

Why it matters Ritual friction drops, legitimacy stays. Still not “the product” by itself — it unlocks trusted rooms.
Pending design

ARCore / ARKit walk assist (supported devices)

Design fit ●●●○○ · Official metre: assist only

Full VIO hit-test + two anchors + world map snapshot while moving, then park and watch. Keep virtual objects near their anchors — a 20 m court needs two ends, not one.

Why it matters Best in-phone map UX where Google/Apple AR runtimes exist. Useless as sole certifier on shiny gym floors.
Pending design

Non-AR walk assist (Camera + IMU)

Design fit ●●○○○ · Official metre: assist only

For phones without ARCore (e.g. RedMagic): CameraX preview + step/stride IMU estimate while walking Line A → Line B. Explicitly drifts. Exists so unsupported devices are not blocked from the ritual.

Why it matters You cannot ship Google’s ARCore device compatibility inside an APK. An in-app walk helper keeps the pathway open without lying about centimetres.

Why the measure table exists

Preferred kit picture from the notes: tape (or laser) owns the metre. Phones sit on the certified lines and watch feet — they do not invent the distance.

Method (good ones only) Official metre Design fit What breaks if you skip honesty
AR walk + steel tape Pass ●●●●● AR-only cm treated as truth → fan-fiction scores
Steel tape / laser only Pass ●●●●○ No camera model of the lines → weaker watch act
Two phones on taped lines Pass ●●●●● No shared audio clock → invented misses
Laser disto / survey wheel Pass ●●●●○ Same as tape if the reading never enters evidence
ARKit / ARCore VIO alone Assist only ●●●○○ ~1–5% scale error; shiny floors; drift
Camera + IMU walk Assist only ●●○○○ Stride error compounds over 20 m; not VIO

Ignored on this board: phone GPS, dual-frequency GNSS, parked phone LiDAR/depth as 20.0 m. See the full table on the notes.

Attempts so far

Each attempt is scored against a pathway above. More code will land here over time.

Attempted

CameraX + IMU walk assist

Pathway: Non-AR walk assist · Android alpha 0.1.2

Certify Course → walk Line A → Line B with camera preview and step/stride (or accel-peak) distance estimate. Adjustable stride (~0.75 m default). Returns an assist estimate into Certify; saving still requires typed tape/laser metres.

  • Ships in-app — no ARCore runtime required (RedMagic-class devices).
  • Evidence can record imuEstimatedMetres separately from certifiedMetres.
  • Honest about drift; not a substitute for preferred walk+tape VIO.
Stub / partial

ARCore measure activity

Pathway: ARCore / ARKit walk assist · optional on supported devices

Optional ARCore Session host and course controller stubs. Manifest marks AR as optional so unsupported phones still install. Full hit-test / GL loop and world-map snapshot still pending design work.

Attempted

Required tape / laser certify field

Pathway: Steel tape / laser only · also the certify step for every other path

Course cannot be saved without certified metres. AR/IMU estimates may display alongside; they never become the official length. This is the minimum honest Path A metre.

Not attempted yet

Two phones + shared beep clock

Pathway: Path C · dual phone

No dual-phone sync, no per-line park flow, no master/slave audio clock in alpha. Called out in-product as “Path C — coming later.”

Not attempted yet

Disto / survey-wheel capture UX

Pathway: Laser disto / survey wheel certify step

Same certify field today; no dedicated disto workflow, Bluetooth meter, or photo-of-reading evidence yet.

Sorry — this download sucks. The Android alpha is a rough debug APK for exercising the attempts above, not a polished store build. Sideload at your own risk; uninstall older alphas if install fights you.

If you still want it: beep-alpha-debug.apk · SHA-256 · current line: Camera + IMU walk assist + optional ARCore stub + required tape certify