OSGEarth的测量分析

我的测量有距离测量、面积测量、高度测量。
测量的结果显示都为一个PlaceNode，可以实时的显示测量的结果。
使用方式为：

pPlaceNode = new osgEarth::Annotation::PlaceNode(
            MapNode, osgEarth::GeoPoint::GeoPoint(), "", textStyle);
pPlaceNode->setDynamic(true);
pPlaceNode->setText("测量结果");
pPlaceNode->setPosition(osgEarth::GeoPoint::GeoPoint(SRS, pos("经纬度")));

• 长度的计算方式使用OSGEarth提供的方式osgEarth::GeoMath::distance()；
• 高度的测量直接两个点的高度差即可；

• 面积的测量，比较麻烦，考虑到需要计算球面的面积，因而需要实现计算方式。附上一个从网上找到的计算方式，由于忘记了原网站，请见谅！

  网上内容，非原创算法
  for (int i = 0; i < iCount; i++)
      {
          if (i == 0)
          {
              //换算成弧度;
              dLowX = osg::DegreesToRadians(points.at(iCount - 1).x());
              dLowY = osg::DegreesToRadians(points.at(iCount - 1).y());
              dMiddleX = osg::DegreesToRadians(points.at(0).x());
              dMiddleY = osg::DegreesToRadians(points.at(0).y());
              dHighX = osg::DegreesToRadians(points.at(1).x());
              dHighY = osg::DegreesToRadians(points.at(1).y());
          }
          else if (i == iCount - 1)
          {
              dLowX = osg::DegreesToRadians(points.at(iCount - 2).x());
              dLowY = osg::DegreesToRadians(points.at(iCount - 2).y());
              dMiddleX = osg::DegreesToRadians(points.at(iCount - 1).x());
              dMiddleY = osg::DegreesToRadians(points.at(iCount - 1).y());
              dHighX = osg::DegreesToRadians(points.at(0).x());
              dHighY = osg::DegreesToRadians(points.at(0).y());
          }
          else
          {
              dLowX = osg::DegreesToRadians(points.at(i - 1).x());
              dLowY = osg::DegreesToRadians(points.at(i - 1).y());
              dMiddleX = osg::DegreesToRadians(points.at(i).x());
              dMiddleY = osg::DegreesToRadians(points.at(i).y());
              dHighX = osg::DegreesToRadians(points.at(i + 1).x());
              dHighY = osg::DegreesToRadians(points.at(i + 1).y());
          }
          AM = cos(dMiddleY) * cos(dMiddleX);
          BM = cos(dMiddleY) * sin(dMiddleX);
          CM = sin(dMiddleY);
          AL = cos(dLowY) * cos(dLowX);
          BL = cos(dLowY) * sin(dLowX);
          CL = sin(dLowY);
          AH = cos(dHighY) * cos(dHighX);
          BH = cos(dHighY) * sin(dHighX);
          CH = sin(dHighY);
  
          dCoefficientL = (AM*AM + BM*BM + CM*CM) / (AM*AL + BM*BL + CM*CL);
          dCoefficientH = (AM*AM + BM*BM + CM*CM) / (AM*AH + BM*BH + CM*CH);
  
          dALtangent = dCoefficientL * AL - AM;
          dBLtangent = dCoefficientL * BL - BM;
          dCLtangent = dCoefficientL * CL - CM;
          dAHtangent = dCoefficientH * AH - AM;
          dBHtangent = dCoefficientH * BH - BM;
          dCHtangent = dCoefficientH * CH - CM;
  
          dAngleCos = (dAHtangent * dALtangent + dBHtangent * dBLtangent + dCHtangent * dCLtangent) /
              (sqrt(dAHtangent * dAHtangent + dBHtangent * dBHtangent + dCHtangent * dCHtangent) *
              sqrt(dALtangent * dALtangent + dBLtangent * dBLtangent + dCLtangent * dCLtangent));
  
          dAngleCos = acos(dAngleCos);
  
          dANormalLine = dBHtangent * dCLtangent - dCHtangent * dBLtangent;
          dBNormalLine = 0 - (dAHtangent * dCLtangent - dCHtangent * dALtangent);
          dCNormalLine = dAHtangent * dBLtangent - dBHtangent * dALtangent;
  
          if (AM != 0)
          {
              dOrientationValue = dANormalLine / AM;
          }
          else if (BM != 0)
          {
              dOrientationValue = dBNormalLine / BM;
          }
          else
          {
              dOrientationValue = dCNormalLine / CM;
          }
          if (dOrientationValue > 0)
          {
              dSum1 += dAngleCos;
              iCount1++;
          }
          else
          {
              dSum2 += dAngleCos;
              iCount2++;
          }
      }
      if (dSum1 > dSum2)
      {
          dSum = dSum1 + (2 * osg::PI*iCount2 - dSum2);
      }
      else
      {
          dSum = (2 * osg::PI*iCount1 - dSum1) + dSum2;
      }
  
      dTotalArea = (dSum - (iCount - 2)*osg::PI)* osg::WGS_84_RADIUS_EQUATOR *
          osg::WGS_84_RADIUS_EQUATOR;
  }