The Parser

Or..."Thank you gencpp for storing everything I need"

In most cases we have access to the Ros Message Type Definition. Luckily for us this string contains all the information we need to know how to deserialize the ROS message. The goal of the parser is to extract the schema and made it available to the user and the deserializer.

This can be simply done calling the function:

  ROSTypeList buildROSTypeMapFromDefinition( const std::string& type_name,
                                             const std::string& msg_definition );

###Example 1

Further we try to parse the type(s) contained in geometry_msgs::Pose

  #include <geometry_msgs/Pose.h>
  // NOTE: in this trivial example we need to include geometry_msgs/Pose
  // even if the main goal of this library is to avoid that.
  
  ///...
  
  using namespace RosIntrospection;
  ROSTypeList typelist = buildROSTypeMapFromDefinition(
                ros::message_traits::DataType< geometry_msgs::Pose >::value(),
                ros::message_traits::Definition< geometry_msgs::Pose >::value());
  std::cout << typelist << std::endl;             

Note that ROSTypeList is a vector of ROSType instances.ROSType itself contains one or more instances of ROSField. Take a look to the API.

The expected output is:

   geometry_msgs/Pose : 
      position : geometry_msgs/Point
      orientation : geometry_msgs/Quaternion

   geometry_msgs/Point : 
      x : float64
      y : float64
      z : float64

   geometry_msgs/Quaternion : 
      x : float64
      y : float64
      z : float64
      w : float64

As expected each message type has a set of fields with a fieldname and a typename.

What is noteworthy is that also all of the non-built-in type in the hierarchy are parsed as well, specifically geometry_msgs/Point and geometry_msgs/Quaternion.

###Example 2

In the next example we will parse all the types found in a single ROS bag. We will not need to #include any of those ROS Types.

To understand this chunk of code you must be familiar with the rosbag::Bag API

  rosbag::Bag bag;
  bag.open( file_name, rosbag::bagmode::Read );

  rosbag::View bag_view ( bag, ros::TIME_MIN, ros::TIME_MAX, true );
  auto first_time = bag_view.getBeginTime();

  const auto& connections = bag_view.getConnections();

  // create a list and a type map for each topic
  std::map<std::string, RosIntrospection::ROSTypeList> type_map;

  for(unsigned i=0; i<connections.size(); i++)
  {
     auto topic_map = buildROSTypeMapFromDefinition( connections[i]->datatype,
                                                     connections[i]->msg_def);
                                                     
     type_map.insert( std::make_pair(connections[i]->topic, topic_map));
  }