//各种标志物类型的定义，每一个的具体介绍和形状可以到这里查看：
http: //wiki.ros.org/rviz/DisplayTypes/Marker
https://blog.csdn.net/u013834525/article/details/80447931
https://github.com/PickNikRobotics/rviz_visual_tools
uint8 ARROW=0//箭头
uint8 CUBE=1//立方体
uint8 SPHERE=2//球
uint8 CYLINDER=3//圆柱体
uint8 LINE_STRIP=4//线条（点的连线）
uint8 LINE_LIST=5//线条序列
uint8 CUBE_LIST=6//立方体序列
uint8 SPHERE_LIST=7//球序列
uint8 POINTS=8//点集
uint8 TEXT_VIEW_FACING=9//显示3D的文字
uint8 MESH_RESOURCE=10//网格？
uint8 TRIANGLE_LIST=11//三角形序列
//对标记的操作
uint8 ADD=0
uint8 MODIFY=0
uint8 DELETE=2
uint8 DELETEALL=3
Header header
string ns //命名空间namespace，就是你理解的那样
int32 id //与命名空间联合起来，形成唯一的id，这个唯一的id可以将各个标志物区 分开来，使得程序可以对指定的标志物进行操作
int32 type //类型
int32 action //操作，是添加还是修改还是删除
geometry_msgs/Pose pose # Pose of the object
geometry_msgs/Vector3 scale # Scale of the object 1,1,1 means default (usually 1 meter square)
std_msgs/ColorRGBA color # Color [0.0-1.0]
duration lifetime # How long the object should last before being automatically deleted. 0 means forever
bool frame_locked # If this marker should be frame-locked, i.e. retransformed into its frame every timestep
#Only used if the type specified has some use for them (eg. POINTS, LINE_STRIP, ...)
geometry_msgs/Point[] points//这个是在序列、点集中才会用到，指明序列中每个点的位置
#Only used if the type specified has some use for them (eg. POINTS, LINE_STRIP, ...)
#number of colors must either be 0 or equal to the number of points
#NOTE: alpha is not yet used
std_msgs/ColorRGBA[] colors
# NOTE: only used for text markers
string text
# NOTE: only used for MESH_RESOURCE markers
string mesh_resource
bool mesh_use_embedded_materials