[Udacity FCND] 坐标表示

Posted 2022-01-22 dm1299

• Geodetic Frame
  (r, θ, φ)表示海拔，经度和纬度。
  
  在地球表面ALTITUDE=0
  
• NED Frame (North East Down)
  在NED坐标系中，(x,y,z)表示与takeoff/home-based point的距离。
  之所以z指向下方，是因为航空学中普遍使用右手坐标系。
  如果z指向上方，则称为ECEF Frame。
  
• Geodetic与NED的转换
  UTM坐标表示：在东西走向，全球一共有60个UTM zones，南北走向一共有24个zones。
  
  这里会使用Python的utm库实现转换。

  • 将GPS position (longitude, latitude, altitude) 转换为 local position (north, east, down)

    def global_to_local(global_position, global_home):
        (east_home, north_home, _, _) = utm.from_latlon(global_home[1], global_home[0])
        (east, north, _, _) = utm.from_latlon(global_position[1], global_position[0])                                    
        local_position = numpy.array([north - north_home, east - east_home, -global_position[2]])
        return local_position

  • 将local position (north, east, down) 转换为 global position (long, lat, up)

    def local_to_global(local_position, global_home):
        (east_home, north_home, zone_number, zone_letter) = utm.from_latlon(global_home[1], global_home[0])
        (lat, lon) = utm.to_latlon(east_home + local_position[1], north_home + local_position[0], zone_number, zone_letter)            
        global_position = numpy.array([lon, lat, -local_position[2]])
        return global_position