Measure and LandmarkRef

Measure

public enum Measure: Sendable, Hashable, Codable

Something read from a pose, in degrees.

Case	Result
.angle(a:vertex:b:)	Inner angle at vertex, 0…180.
.flexion(a:vertex:b:)	180 − angle: 0 = straight, grows as it bends.
.fromVertical(from:to:)	Segment against vertical: 0 down, 90 horizontal, 180 up.
.tilt(a:b:)	Line against level: 0 level, 90 vertical.

func value(in pose: Pose, side: BodySide) -> Double?
func joints(for side: BodySide) -> [Joint]

value is nil if a joint is missing or two points coincide.

let flexion = Measure.flexion(a: "hip", vertex: "knee", b: "ankle")
flexion.value(in: pose, side: .left)   // e.g. 87.4
flexion.joints(for: .left)             // [.leftHip, .leftKnee, .leftAnkle]

2D coordinates

Measures are taken in the image plane. A movement toward the camera looks shorter than it is; that’s why each exercise declares its view, and SetupCheck warns if the patient isn’t facing the right way.

LandmarkRef

public struct LandmarkRef: Sendable, Hashable, Codable, ExpressibleByStringLiteral

A body point relative to the exercised side, so one exercise works for both sides.

Text	Meaning with side = .left
"elbow"	.leftElbow
"opposite.shoulder"	.rightShoulder
"neck"	.neck (midline: never changes)

Points: nose, neck, root, eye, ear, shoulder, elbow, wrist, hip, knee, ankle.

LandmarkRef(.shoulder, opposite: true)
LandmarkRef(string: "opposite.hip")   // nil if not recognized
ref.joint(for: .right)
ref.stringValue                        // "opposite.hip"

In JSON it’s a String. An unknown literal in Swift ("elbw") stops execution with preconditionFailure; in JSON it produces a DecodingError.