feat(v2): add fall event regression engine

v2/internal/fall/evidence.go

@@ -0,0 +1,62 @@
+package fall
+
+import (
+	"math"
+
+	"silverpose/v2/internal/pose"
+)
+
+var torsoJoints = [...]int{5, 6, 11, 12}
+var lowerJoints = [...]int{13, 14, 15, 16}
+
+func assessPoseQuality(person pose.PersonPose, threshold float32, requireLowerBody bool) PoseQuality {
+	if threshold < 0 || threshold > 1 {
+		return PoseQuality{Reason: "invalid_threshold"}
+	}
+	visible := 0
+	for _, keypoint := range person.Keypoints {
+		if keypoint.Confidence >= threshold {
+			visible++
+		}
+	}
+	for _, index := range torsoJoints {
+		if person.Keypoints[index].Confidence < threshold {
+			return PoseQuality{Reason: "required_joint_low_confidence", VisibleJointCount: visible}
+		}
+	}
+	if requireLowerBody {
+		for _, index := range lowerJoints {
+			if person.Keypoints[index].Confidence < threshold {
+				return PoseQuality{Reason: "required_joint_low_confidence", VisibleJointCount: visible}
+			}
+		}
+	}
+	return PoseQuality{Accepted: true, Reason: "accepted", VisibleJointCount: visible}
+}
+
+func extractEvidence(person pose.PersonPose, quality PoseQuality, previous *PoseEvidence, horizontalAngleThreshold float32) PoseEvidence {
+	if !quality.Accepted {
+		return PoseEvidence{Reason: quality.Reason}
+	}
+	shoulderX, shoulderY := midpoint(person, 5, 6)
+	hipX, hipY := midpoint(person, 11, 12)
+	vectorX := hipX - shoulderX
+	vectorY := hipY - shoulderY
+	torsoLength := float32(math.Hypot(float64(vectorX), float64(vectorY)))
+	if torsoLength == 0 {
+		return PoseEvidence{HipCenterY: hipY, HasHipCenterY: true, TorsoLength: 0, Reason: "degenerate_torso"}
+	}
+	cosine := math.Max(-1, math.Min(1, math.Abs(float64(vectorX))/float64(torsoLength)))
+	angle := float32(math.Acos(cosine) * 180 / math.Pi)
+	rapid := previous != nil && previous.Accepted && previous.HasHipCenterY && hipY-previous.HipCenterY >= 0.5*torsoLength
+	return PoseEvidence{
+		Accepted: true, HorizontalPose: angle <= horizontalAngleThreshold,
+		RapidVerticalChange: rapid, HorizontalAngleDegree: angle, HasAngle: true,
+		HipCenterY: hipY, HasHipCenterY: true, TorsoLength: torsoLength, Reason: "accepted",
+	}
+}
+
+func midpoint(person pose.PersonPose, first, second int) (float32, float32) {
+	return (person.Keypoints[first].X + person.Keypoints[second].X) / 2,
+		(person.Keypoints[first].Y + person.Keypoints[second].Y) / 2
+}