When a pose comes out twisted, mirrored, or drifting we debug it by permuting signs until it looks right. That means wrong fixes survive. This course replaces sign-permutation with reasoning you can check against a specification. See MISSION.md for what we are aiming at.
Work through the lessons in any order. Each is short, self-contained, and ends with a quiz.
The reference sheets compress each lesson into a cheat sheet.
Planned, in roughly this order. Four main failure classes: twisted limbs, mirrored motion, multiply-order confusion, and drift.
| Next | Skill it buys you |
|---|---|
| 002 · The rotation that follows the flip | See a reflection reverse the sense of a rotation, so the quaternion rule stops being a memorised sign pattern. Closes out the mirrored-motion bug. |
| 003 · Local, world, and which side to multiply on | Read T * R * S and parent * local
and know what each product means — the highest-frequency confusion of the four. |
| 004 · Reading a quaternion by eye | Recover axis and angle from four numbers; know why q and −q
are the same rotation and when that bites. |
| 005 · Building a basis from three points | The optical/vision spine: turn joint positions into a frame, and orthonormalize it without introducing a twist. |
| 006 · Sensor-to-segment calibration | See the calibration offset as a fixed change of basis rather than a magic quaternion. This is the twisted-limb bug. |
| 007 · Drift, normalization, and reference frames | Why poses degrade, why gravity is a reference frame, and what a T-pose calibration actually pins down. |
lessons/ | One self-contained HTML page per lesson. Start here. |
reference/ | Printable cheat sheets — the compressed, durable part. |
assets/ | Shared components: the stylesheet, a dependency-free 3D renderer, the convention definitions, controls, and the quiz widget. |
assets/brand/ | The Impractical Instruments design system — tokens and fonts, vendored verbatim so the course still opens offline. |
MISSION.md | Why we are learning this. Every lesson traces back to it. |
GLOSSARY.md | The canonical vocabulary. Lessons adhere to it. |
RESOURCES.md | Trusted sources, annotated — plus explicit gaps. |
learning-records/ | What the team has established, and what that changes about what to teach next. |
NOTES.md | Teaching preferences and working notes. |