fix(prediction): geo.ts 중복 함수 제거 및 null 좌표 참조 오류 수정

frontend/src/common/utils/geo.ts

@@ -299,23 +299,6 @@ export function pointInPolygon(
   return inside
 }
 
-/** 다각형 면적 (km²) — Shoelace formula, 구면 보정 포함 */
-export function polygonAreaKm2(polygon: { lat: number; lon: number }[]): number {
-  if (polygon.length < 3) return 0
-  const n = polygon.length
-  const latCenter = polygon.reduce((s, p) => s + p.lat, 0) / n
-  const cosLat = Math.cos(latCenter * DEG2RAD)
-  let area = 0
-  for (let i = 0; i < n; i++) {
-    const j = (i + 1) % n
-    const x1 = polygon[i].lon * cosLat * EARTH_RADIUS * DEG2RAD / 1000
-    const y1 = polygon[i].lat * EARTH_RADIUS * DEG2RAD / 1000
-    const x2 = polygon[j].lon * cosLat * EARTH_RADIUS * DEG2RAD / 1000
-    const y2 = polygon[j].lat * EARTH_RADIUS * DEG2RAD / 1000
-    area += x1 * y2 - x2 * y1
-  }
-  return Math.abs(area) / 2
-}
 
 /** 원 면적 (km²) */
 export function circleAreaKm2(radiusM: number): number {

frontend/src/tabs/prediction/components/OilSpillView.tsx

@@ -207,9 +207,10 @@ export function OilSpillView() {
   useEffect(() => {
     if (activeSubTab === 'analysis' && oilTrajectory.length === 0 && !selectedAnalysis) {
       const models = Array.from(selectedModels.size > 0 ? selectedModels : new Set<PredictionModel>(['OpenDrift']))
-      const demoTrajectory = generateDemoTrajectory(incidentCoord, models, predictionTime)
+      const coord = incidentCoord ?? { lat: 37.39, lon: 126.64 }
+      const demoTrajectory = generateDemoTrajectory(coord, models, predictionTime)
       setOilTrajectory(demoTrajectory)
-      const demoBooms = generateAIBoomLines(demoTrajectory, incidentCoord, algorithmSettings)
+      const demoBooms = generateAIBoomLines(demoTrajectory, coord, algorithmSettings)
       setBoomLines(demoBooms)
       setSensitiveResources(DEMO_SENSITIVE_RESOURCES)
     }