/** 获得地面当前点的插值高度 */
float getAveHeight(float x,float z)
{
     float CameraX, CameraZ;
     CameraX = x / m_nCellWidth;
     CameraZ = z / m_nCellWidth;
     /** 计算高程坐标(Col0, Row0)，(Col1, Row1) */
     int col0 = int(CameraX);
     int row0 = int(CameraZ);
     unsigned int col1 = col0 + 1;
     unsigned int row1 = row0 + 1;
     /** 确保单元坐标不超过高程以外 */
     if (col1 > m_nWidth) col1 = 0;
     if (row1 > m_nWidth) row1 = 0;
     /** 获取单元的四个角的高度 */
     float h00 = (float)(m_pHeightMap[col0*m_nCellWidth + row0*m_nCellWidth*m_nWidth]);
     float h01 = (float)(m_pHeightMap[col1*m_nCellWidth + row0*m_nCellWidth*m_nWidth]);
     float h11 = (float)(m_pHeightMap[col1*m_nCellWidth + row1*m_nCellWidth*m_nWidth]);
     float h10 = (float)(m_pHeightMap[col0*m_nCellWidth + row1*m_nCellWidth*m_nWidth]);
     /** 计算机摄像机相对于单元格的位置 */
     float tx = CameraX - int(CameraX);
     float ty = CameraZ - int(CameraZ);
     /** 进行双线性插值得到地面高度 */
     float txty = tx * ty;
     float final_height     = h00 * (1.0f - ty - tx + txty)
                              + h01 * (tx - txty)
                              + h11 * txty
                              + h10 * (ty - txty);
     return final_height;
}

     float tx = CameraX - int(CameraX);
     float ty = CameraZ - int(CameraZ);