ROS:绘制 GPS 轨迹
该功能绘制实时GPS数据信息，并且在rviz2中展示出来。
1、实现原理
GPS的信息直接可视化是不可能，我们需要转换下坐标系，将GPS轨迹，从经纬度WGS-84坐标转换到真实世界xyz坐标系下。有了在真实世界的xyz坐标，我们就可以通过rviz2去显示路径，模拟出是GPS的轨迹。轨迹就是累计每个gps坐标相对与第一个坐标的位置，然后累加即可得到轨迹。
2、启动步骤
终端输入，
ros2 launch nmea_navsat_driver gps_path_to_rviz.launch.py
在rviz2显示的界面，我们可以看到，绿色的线在不断慢慢地延伸，如下图所示，
3、launch代码解析
python
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node
from ament_index_python.packages import get_package_share_directory
import os
def generate_launch_description():
port_arg = DeclareLaunchArgument('port', default_value='/dev/myserial')
baud_arg = DeclareLaunchArgument('baud', default_value='9600')
frame_id_arg = DeclareLaunchArgument('frame_id', default_value='gps')
time_ref_source_arg = DeclareLaunchArgument('time_ref_source', default_value='gps')
useRMC_arg = DeclareLaunchArgument('useRMC', default_value='False')
port = LaunchConfiguration('port')
baud = LaunchConfiguration('baud')
frame_id = LaunchConfiguration('frame_id')
time_ref_source = LaunchConfiguration('time_ref_source')
useRMC = LaunchConfiguration('useRMC')
nmea_serial_driver_node = Node(
package='nmea_navsat_driver',
executable='nmea_serial_driver',
name='nmea_serial_driver_node',
output='screen',
parameters=[{
'port': port,
'baud': baud,
'frame_id': frame_id,
'time_ref_source': time_ref_source,
'useRMC': useRMC
}]
)
gps_path_node = Node(
package='nmea_navsat_driver',
executable='Draw_GPS_Path',
name='gps_path_node',
output='screen'
)
rviz_config = os.path.join(
get_package_share_directory('nmea_navsat_driver'),
'rviz',
'gps_path.rviz'
)
rviz_node = Node(
package='rviz2',
executable='rviz2',
name='rviz2',
arguments=['-d', rviz_config]
)
return LaunchDescription([
port_arg,
baud_arg,
frame_id_arg,
time_ref_source_arg,
useRMC_arg,
nmea_serial_driver_node,
gps_path_node,
rviz_node
])启动了三个节点，分别是nmea_serial_driver_node读取GPS数据、gps_path_node绘制GPS数据轨迹和rviz2节点。
其中，gps_path_node这个节点的源码gps_path.cpp在nmea_navsat_driver/src下，可以去看看。