Androidは百度の地図を使って多角形の面積を測定します

btn_clear = (Button)findViewById(R.id.btn_clear);
btn_jisuan = (Button)findViewById(R.id.btn_jisuan);
//      
mMapView = (MapView) findViewById(R.id.mapView);
mBaiduMap = mMapView.getMap();
//        
mBaiduMap.setOnMapClickListener(new OnMapClickListener() {
			@Override
			public boolean onMapPoiClick(MapPoi arg0) {
				return false;
			}
			@Override
			public void onMapClick(final LatLng latLng) {
				//       
				latitude = latLng.latitude;  
				longitude = latLng.longitude; 
				//   Maker     
				LatLng point = new LatLng(latitude, longitude);  

				MarkerOptions options = new MarkerOptions().position(point).icon(icon_muasure); 
				pts.add(latLng);
				//       Marker，     
				mBaiduMap.addOverlay(options);
				
			}
		});


//        
btn_jisuan.setOnClickListener(new OnClickListener() {
	@Override
	public void onClick(View v) {
		String area = getArea(pts);
		//        
 		OverlayOptions ooText = new TextOptions().bgColor(0xAAFFFF00)
	                .fontSize(48).fontColor(0xFFFF00FF).text("  ：" + area + " m²")
	                .position(pts.get(0));
	        mBaiduMap.addOverlay(ooText);
	}
});
//        
btn_jisuan.setOnClickListener(new OnClickListener() {
	@Override
	public void onClick(View v) {
		pts.clear();
		mBaiduMap.clear();
	}
});



	/**
	 *        
	 * @return 
	 */
	protected String getArea(List<LatLng> pts) {
		double totalArea = 0;//       
		double LowX = 0.0; 
		double LowY = 0.0; 
		double MiddleX = 0.0;
		double MiddleY = 0.0;
		double HighX = 0.0;
		double HighY = 0.0;
		double AM = 0.0;
		double BM = 0.0;
		double CM = 0.0;
		double AL = 0.0;
		double BL = 0.0;
		double CL = 0.0;
		double AH = 0.0;
		double BH = 0.0;
		double CH = 0.0;
		double CoefficientL = 0.0;
		double CoefficientH = 0.0;
		double ALtangent = 0.0;
		double BLtangent = 0.0;
		double CLtangent = 0.0;
		double AHtangent = 0.0;
		double BHtangent = 0.0;
		double CHtangent = 0.0;
		double ANormalLine = 0.0;
		double BNormalLine = 0.0;
		double CNormalLine = 0.0;
		double OrientationValue = 0.0;
		double AngleCos = 0.0;
		double Sum1 = 0.0;
		double Sum2 = 0.0;
		double Count2 = 0;
		double Count1 = 0;
		double Sum = 0.0;
		double Radius = 6378137.0;// WGS84    
		int Count = pts.size();
		//  3  
		if (Count  < 3) {
			return;
		}
		for ( int i = 0; i < Count; i++) {
			if (i == 0) {
				LowX = pts.get(Count - 1).longitude * Math.PI / 180;
				LowY = pts.get(Count - 1).latitude * Math.PI / 180;
				MiddleX = pts.get(0).longitude * Math.PI / 180;
				MiddleY = pts.get(0).latitude * Math.PI / 180;
				HighX = pts.get(1).longitude * Math.PI / 180;
				HighY = pts.get(1).latitude * Math.PI / 180;
			} else if (i == Count - 1) {
				LowX = pts.get(Count - 2).longitude * Math.PI / 180;
				LowY = pts.get(Count - 2).latitude * Math.PI / 180;
				MiddleX = pts.get(Count - 1).longitude * Math.PI / 180;
				MiddleY = pts.get(Count - 1).latitude * Math.PI / 180;
				HighX = pts.get(0).longitude * Math.PI / 180;
				HighY = pts.get(0).latitude * Math.PI / 180;
			} else {
				LowX = pts.get(i - 1).longitude * Math.PI / 180;
				LowY = pts.get(i - 1).latitude * Math.PI / 180;
				MiddleX = pts.get(i).longitude * Math.PI / 180;
				MiddleY = pts.get(i).latitude * Math.PI / 180;
				HighX = pts.get(i + 1).longitude * Math.PI / 180;
				HighY = pts.get(i + 1).latitude * Math.PI / 180;
			}
			AM = Math.cos(MiddleY) * Math.cos(MiddleX);
			BM = Math.cos(MiddleY) * Math.sin(MiddleX);
			CM = Math.sin(MiddleY);
			AL = Math.cos(LowY) * Math.cos(LowX);
			BL = Math.cos(LowY) * Math.sin(LowX);
			CL = Math.sin(LowY);
			AH = Math.cos(HighY) * Math.cos(HighX);
			BH = Math.cos(HighY) * Math.sin(HighX);
			CH = Math.sin(HighY);
			CoefficientL = (AM * AM + BM * BM + CM * CM)/ (AM * AL + BM * BL + CM * CL);
			CoefficientH = (AM * AM + BM * BM + CM * CM)/ (AM * AH + BM * BH + CM * CH);
			ALtangent = CoefficientL * AL - AM;
			BLtangent = CoefficientL * BL - BM;
			CLtangent = CoefficientL * CL - CM;
			AHtangent = CoefficientH * AH - AM;
			BHtangent = CoefficientH * BH - BM;
			CHtangent = CoefficientH * CH - CM;
			AngleCos = (AHtangent * ALtangent + BHtangent * BLtangent + CHtangent* CLtangent)/ (Math.sqrt(AHtangent * AHtangent + BHtangent* BHtangent 

+ CHtangent * CHtangent) * Math.sqrt(ALtangent * ALtangent + BLtangent* BLtangent + CLtangent * CLtangent));
			AngleCos = Math.acos(AngleCos);
			ANormalLine = BHtangent * CLtangent - CHtangent * BLtangent;
			BNormalLine = 0 - (AHtangent * CLtangent - CHtangent* ALtangent);
			CNormalLine = AHtangent * BLtangent - BHtangent * ALtangent;
			if (AM != 0)
				OrientationValue = ANormalLine / AM;
			else if (BM != 0)
				OrientationValue = BNormalLine / BM;
			else
				OrientationValue = CNormalLine / CM;
			if (OrientationValue > 0) {
				Sum1 += AngleCos;
				Count1++;
			} else {
				Sum2 += AngleCos;
				Count2++;
			}
		}

		double tempSum1, tempSum2;
		tempSum1 = Sum1 + (2 * Math.PI * Count2 - Sum2);
		tempSum2 = (2 * Math.PI * Count1 - Sum1) + Sum2;
		if (Sum1 > Sum2) {
			if ((tempSum1 - (Count - 2) * Math.PI) < 1)
				Sum = tempSum1;
			else
				Sum = tempSum2;
		} else {
			if ((tempSum2 - (Count - 2) * Math.PI) < 1)
				Sum = tempSum2;
			else
				Sum = tempSum1;
		}
		totalArea = (Sum - (Count - 2) * Math.PI) * Radius * Radius;

		return String.valueOf(Math.floor(totalArea)); //      
	}

効果図:
注意:このアルゴリズムはたまに面積が負の場合がありますが、まだ解決されていません.
参考記事:http://blog.csdn.net/chenguang79/article/details/40506469