# Method A / B / C Algorithm Comparison & Placement Test

_마지막 업데이트: 2026-07-13 — V2 6-stage / CH3 flicker 3-Layer 반영._

## Wall Detection Comparison

### Pipeline

```
Method A:  raw → SG → composite(sg+|d1|+|d2|) → plateau score → plateau spans
           → prominence wall (ANT=nearest, POST=edge_score)
           → cross-validation → BV(frustum+ellipse cap, 1ch=sphere)
           ※ 채널별 min_wall_contrast_ratio × cos(θ) 보정

Method B:  raw → SG → TGC(multichannel log-fit) → initial detect(Otsu×0.9×cos(θ))
           → BR candidate(per-ch, post-only, prominence≥50)
           → consensus(median, outlier_tol=4, min_votes=3)
           → is_reflection_only(shared+cluster, amp_ratio=1.5)
           → resolve(suspicious post: post>ant×1.5)
           → suppress(valley early-stop 50.0) → rerun detect
           → choose(rerun vs initial) → BV(frustum+ellipse cap, 1ch=sphere)

Method C:  raw → MedianFilter(win=7) → SG+wavelet
           → ImpulseReject(2-pass Hampel, lumen clean)
           → OS-CFAR(per-sample) → lumen mask
           → prominence wall + subsample refine
           → StaLta impulse purity check
           → anatomical gate (antDepth≥10mm, chord 5-110mm)
           → BModeScore V41 (wamp=0.45, stalta=0.20, far=0.15, dark=0.10)
           → ChordConsensus (Tukey MAD + Fischler-Bolles pair test)
           → BV dispatch(frustum/chord/sphere, trusted channels only)
```

### Stage-by-Stage

| Stage | **A (Plateau)** | **B (Otsu+TGC+BR)** | **C (V4.1 CFAR)** |
|-------|-----------------|----------------------|---------------------|
| Pre-filter | none | none | MedianFilter(win=7) + ImpulseReject(Hampel) |
| Denoising | SG(5,2) | SG(5,2) → log-TGC | SG(5,2) + db4 wavelet 3-level |
| Threshold | sliding plateau score Q=0.5 | Otsu×0.9×cos(θ) | OS-CFAR (win=15, rank=40%, scale=1.05) |
| Low-echo mask | platScore < thr | sg <= otsu (full) | sg <= median(CFAR) |
| Span merge | gap≤5, simple | gap<3: unconditional, ≥3: wall check | mergeGapMax=5, gapPeakMargin=50 |
| Span refine | none | refineRightEdge | none |
| Wall select | ANT=nearest, POST=edge_score, decay=0.15 | ANT=nearest, POST=edge_score, decay=0.12 | prominence + subsample, MAX_CANDIDATES_POST=64 |
| Valley logic | descending-first, rise=5 | descending-first, rise=50 | rise=50 |
| Extra conditions | contrast×cos(θ)≥1.2, prom≥3 | peakMin=max(low+30,thr), sg[ant/post]≥thr, postProm≥30 | Kremkau ant fallback, antMinIdx=7 |
| Score | sg[ant]+sg[post] | asymmetric ant_reliability | BModeScore V41 (wamp+stalta+far+dark+grad) |
| FP filter | cross-validation | score<3000 | AnatomicalGate + ChordConsensus |
| Impulse check | none | none | StaLta (STA/LTA ratio) |
| Channel filter | none | none | ChordConsensus (MAD outlier + pair test) |
| Back reflection | none | consensus multichannel BR | none |
| Fallback | none | ant=max(0,s-(post-e)) | B-mode tier |

### BV Estimation

| | **A** | **B** | **C** |
|---|---|---|---|
| Model | shared with B | frustum + ellipse cap | Multi-dispatch (trusted ch only) |
| 1-channel | sphere V=(4/3)πR³ | same | Verathon chord |
| Channel filter | none | none | ChordConsensus (drop inconsistent) |
| Cap height | 8-point ellipse LSQ | same | fixed: bottom=hemisphere, top=cone |
| LR ratio | shared with B | 2-lateral ellipse solve + shrinkage | 1/avg_ratio, clamp[1.0,1.6] |
| Confidence | none | none | 0.95(4C+2L) ~ 0.20(1ch) |
| DPS | PiezoHW (1.968) | same | 1.9309 |

### Angle Correction (PR#20)

Both Method A and B apply per-channel beam angle correction:
- **Method B**: `otsu_ratio = OTSU_RATIO × cos(θ)` per channel
- **Method A**: `min_wall_contrast_ratio = 1.2 × cos(θ)` per channel
- Larger angles → lower threshold → better detection of weak posterior walls

### Back Reflection System (Method B)

```
Per-channel:
  1. initial detect → (ant, post)
  2. build_candidate: strongest peak AFTER post (prominence≥50)
     - global BR ≈ post (±3) → None (no separate BR)
     - else → strongest significant peak after post

Multichannel:
  3. consensus: median, outlier_tol=4, min_votes=3
  4. is_reflection_only: post > ant × 1.5 (amp_ratio)
     - Condition A: shared_idx based
     - Condition B: post cluster based

Per-channel resolve:
  5. is_suspicious_post: post > ant × 1.5 OR post ≈ shared (±2)
  6. select_idx → resolve → suppress(valley early-stop 50.0)
  7. rerun detect → choose(rerun vs initial, min_gap=8)
```

### Method C V4.1 New Features (2026-05-04)

```
Pre-processing:
  MedianFilter(win=7) → remove speckle bumps
  ImpulseReject(2-pass Hampel) → clean 1-3 sample impulses in lumen

Detection:
  DetectLumenFirst V41_PARAMS:
    mergeGapMax=5, gapPeakMargin=50
    maxCandidatesPost=64, medianWin=7, antMinIdx=7
    Kremkau half-amplitude ant fallback

Quality:
  StaLta: STA/LTA ratio → wall edge vs reverberation discrimination
  BModeScore V41_WEIGHTS:
    wamp=0.45 (wall-peak amplitude)
    stalta=0.20 (impulse purity)
    far=0.15, dark=0.10, ant=0.05, post=0.05

Channel Filtering:
  ChordConsensus: Tukey MAD outlier + Fischler-Bolles pair test
  → drop geometrically inconsistent channels before BV

Anatomical Gate:
  antDepthMin: 22 → 10mm (Neyman-Pearson loose prior)
  strict threshold removed → delegated to B-mode score
```

---

## Python vs Kotlin Sync Status (2026-05-04)

### Method A/B: 18 functions compared — CRITICAL 0, MINOR 5

All config constants match: LOW_ECHO_AMP=1250, OTSU_RATIO=0.9, MIN_SCORE=3000,
EDGE_DIST_DECAY=0.12, VALLEY_STOP_RISE=50, etc.

### Method C: Direct copy from CharlesKWONsLaw (45 files, package renamed)

---

## Placement Test Algorithm

### Overview (2026-05-26 updated — v6)

```
Screen entry → "Place VesiScan above the pubic bone, then press Start"
    ↓ Start Alignment 버튼 탭 (waitingForStart=false)
전체 상태 리셋
    ↓
[600ms interval loop]  ← v6: 1000ms → 600ms (BleManager throttle과 동기화)
    ↓
mpa (first time, 500ms delay) → maa → 6ch reb
    ↓ (maa 전 BleManager.canSendMaa() 게이트 통과 필요)
    │   - State gate: !piezoCollector.isComplete 이면 차단 (3s 후 FORCE)
    │   - Time gate: 마지막 송신 < 600ms 이면 차단
    │
Detachment check (6ch received, THR=30) → LED 4 if detached
    ↓
Wall detection (Method A/B/C) → urineLen ≥ 12
    ↓
computePlacementGuide() → 3-stage guide (VERTICAL → LATERAL → GREEN)
    ↓
Debounce (2 consecutive + 1.5s/3s hold) + Phase protection (3 scans)
    ↓
Arrow direction: always updated (directionIcon synced with guideResult)
    ↓
LED: stage change only (4=detach, 5=searching, 6=complete)
    ↓
GREEN: 7s hold + 3 consecutive fail to exit
    ↓
Screen exit → LED OFF
```

### v6 BLE 사이클 실측 (VBTFW0116 + MTU 247 + CONN_PRIORITY HIGH)

한 측정 사이클 (TX maa → RX raa): **평균 ~330ms** (이전 ~1.2~1.4s 대비 4배 향상).
600ms loop delay 안에 한 사이클이 안정적으로 완료됨.

### Guide Modes

**Gradient** (default): weighted center gradient → LATERAL → GREEN
**Boundary**: up → detect boundary (max drops) → come back → LATERAL
**SWEEP** (CKLaw): navel → slide down → sagittalArgMaxCh → LATERAL → GREEN

### 3-Stage Guide (V1 — 일반 사용자 진입, `computePlacementGuide`)

**Stage 1 VERTICAL**: detect count + gradient + "Slide up/down ↑↓"
**Stage 2 LATERAL**: |len4-len5| ≤ 10 → GREEN, else "Slide left/right ←→"
**Stage 3 GREEN**: CV ≤ threshold AND |LR dev| ≤ 0.20 → "In position!" (7s hold)

### 6-Stage Guide (V2 — Clinical Alignment 세션, `AlignGuide4Stage`)

`ClinicalHome → Sensor Alignment` 진입 시 자동 활성화. Method D chord 기반
CV 로 정밀 vertical 조정 + CH3 flicker 대응 sliding-window majority.

| # | Phase | 조건 |
|:---:|---|---|
| 1 | INITIAL_ACCUM | baseline 10 cycle 누적 |
| 2 | VERTICAL_CLIMB | CH3 sliding window majority — 최근 6 프레임 중 hit ≥ 3 |
| 3 | CH3_STABILIZE | 10 cycle 위치 유지, lost 판정도 sliding (window=4, majority=3) |
| 4 | CENTER_OPTIMIZE | CH0~CH3 chord CV ≤ 0.15 (3연속 hysteresis) |
| 5 | LR_BALANCE | \|u4−u5\| ≤ 8 samples, lost 채널 3연속 hysteresis |
| 6 | FINAL_CONFIRM | buf clear → 5 fresh 프레임 재확인 통과 → GREEN |

**CH3 flicker 대응 3-Layer** (2026-07-06 이후, commit e808b5b / 9261bc7 / 4f8d536):
- **Layer 1 — Sliding-Window Majority**: 3 연속 hit 대체. 인체 flick 패턴
  (YYNNYY 등) 통과 가능.
- **Layer 2 — Stuck Detection + Relaxed Mode**: VERTICAL_CLIMB 20 프레임 (~5초)
  갇힘 + CH3 hit 저조 + CH0~CH2 all detected → CH3 없이 상단 3채널로 CENTER_OPT
  진입 허용. `AlignmentConstants.VERTICAL_STUCK_THRESHOLD`.
- **Layer 3 — UX Soft-Hint**: 12 프레임 (~3초) 반복 시 "↑ 위로" →
  "CH3 신호 확인 중 · 위치 유지" 로 문구 자동 완화.

**Python replay 검증** (`tools/align_analyze.py`, 2026-07-10~13): data123/ 인체
4 세션 (Phantom + Human 0/1/3 CM). NEW vs LEGACY 병행 replay 결과 Human 0CM
(CH3 31.8%) 회귀 방지 + Human 1CM (77.3%) 조기 진입 확인, 팬텀 false-positive
없음. 상세 표: `tools/README.md`.

### Measurement Modes (v6 업데이트)

- **Auto Scan**: **min 600ms gap** (state-based throttle: `!isComplete` + 600ms), 10-sample trimmed mean (max/min removed, 8 avg)
- **Single Scan (Spot)**: 5회 측정 → trimmed mean (max 8 attempts, min 3)
- valid ≥ 4 channels only
- Analysis on coroutine (Dispatchers.Default)
- Auto fail: 2ch+ missing 5 consecutive → realign dialog
- **Voiding/Catheterization 클릭 시 Auto Scan 자동 stop + 측정 상태 정규화** (displayMaxVolumeMl/window/timer 모두 0)
- Detachment → LED 4 (once), recovery → LED 0 (once)
- Foreground Service: BLE connection maintained during screen off
- BLE 로그: 실시간 파일 기록 (Downloads/VesiScan_BLE_*.log, 화면 잠금에도 보존)
- CSV: 세션별 파일 (YYYY-MM-DD_HHmmss.csv)

### Placement GREEN 기준

```
CV threshold = DEFAULT_CV_THR + (scanCount / 5) × 0.03
  DEFAULT_CV_THR: V0=0.07, V1/V2=0.10, 기타=0.08
LR deviation ≤ 0.20
GREEN hold: 7초 (greenLockedAtMs 기준)
GREEN exit: 3회 연속 실패 (greenFailCount)
```

### Test Results (2026-05-04, 500ml phantom, Method C V4.1)

```
총 측정: 223회
평균: 492.4ml (오차 -1.5%)
±15% 이내: 223/223 (100%)
범위: 441~537ml
```

---

## BLE maa Throttle — State-Based Gate (v6, 2026-05-26)

### 배경: CH0/CH1만 도착 + BV_FAIL/BV_SKIP 증상

이전 throttle은 시간 단독 `now - lastMaaSentMs < 800ms` 만 검사. 펌웨어 응답이
~1.2~1.4초 걸리는 환경에서 800ms 시점에 새 maa가 송신되면:

1. `sendChannelsOnly()` 통과 → `piezoCollector.startMultiChannel(6)` → collector reset
2. **큐에 떠다니던 이전 사이클의 reb / raa 패킷이 새 collector의 시작 부분에 잘못 들어감**
3. 결과: 한 채널만 들고 raa로 종료 → `BV_FAIL no valid channels` 또는 `BV_SKIP center=0 total=5/6`

실측 로그 (FW VBTFW0111, 2026-05-22):
```
TX maa #1     → reb×5 → (raa 큐 밀림) → TX maa #2 → reb×1 + raa → BV_FAIL scan=656
```

### v6 신규 게이트

```kotlin
private fun canSendMaa(caller: String): Boolean {
    val now = System.currentTimeMillis()
    val collectorBusy = piezoCollector.isMultiChannel && !piezoCollector.isComplete
    val sinceLast = now - lastMaaSentMs
    if (collectorBusy) {
        if (sinceLast < 3000) return false                       // (A) state 차단
        // 3s 넘으면 강제 통과 (FORCE) — deadlock 방지
    }
    if (sinceLast < 600) return false                            // (B) time 차단
    return true
}
```

| 게이트 | 차단 | 풀림 |
|---|---|---|
| (A) State | `isMultiChannel && !isComplete` | raa 도착 OR 3s FORCE |
| (B) Time | `sinceLast < 600` | 600ms 경과 |

두 게이트 모두 통과해야 maa 송신. State gate가 race 방어, time gate가 burst 방어.

### 효과 (FW VBTFW0116 + MTU 247 + CONN_PRIORITY HIGH 조합)

- 한 사이클 응답: 1.2s → **330ms** (4배)
- 6/6 채널 도착률: 부분응답 잦음 → **100% 도착, 유실 0건**
- BV_FAIL/BV_SKIP 빈도: 자주 → 관찰되지 않음

### Logcat 키워드

| 로그 | 의미 |
|---|---|
| `maa BUSY [...] — prev response in progress (Xms)` | State gate 차단 (정상 방어) |
| `maa FORCE [...] — prev incomplete after Xms` | 3s 넘게 raa 없음 → 포기하고 진행 |
| `maa THROTTLED [...] — Xms since last` | Time gate 차단 (정상 방어) |
| (로그 없음) | 정상 송신 |
| `MTU changed: 247 (status=0)` | MTU 정상 협상 (CCCD write 직전) |
| `CONN_PRIORITY HIGH requested (ok=true)` | priority 요청 큐잉 성공 (수락 여부는 sniffer로만 확인 가능) |