tf2::toMsg

tf2::toMsg是ROS中的一个函数，它可以将tf2中的Transform类型转换成ROS中的geometry_msgs::TransformStamped类型。这个函数在使用tf2库时非常有用，因为在ROS中，我们经常需要对不同坐标系下的数据进行转换。而tf2库就是用来实现这种转换的。通过使用tf2::toMsg函数，我们可以将tf2中的Transform类型转换成可发布到ROS话题上的消息类型，以便其他节点订阅并进行进一步处理。

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tf2::toMsg 头文件

tf2::toMsg 是一个函数模板，它将一个类型为 tf2::Transform 或 tf2::StampedTransform 的转换为 ROS 消息。这个函数模板定义在 tf2_geometry_msgs 库的头文件中，可以使用它来将 tf2::Transform 和 tf2::StampedTransform 转换为不同类型的 ROS 消息，比如 geometry_msgs::TransformStamped 和 geometry_msgs::PoseStamped。这个函数模板的定义如下：

template <typename T>
void toMsg(const tf2::Transform& transform, T& msg);

其中，第一个参数是要转换的 Transform，第二个参数是转换后的消息。这个函数模板会根据第二个参数的类型自动选择转换方式。需要注意的是，转换后的消息必须已经被正确初始化。

给下列程序添加英文注释：bool MoveBase::getRobotPose(geometry_msgs::PoseStamped& global_pose, costmap_2d::Costmap2DROS* costmap) { tf2::toMsg(tf2::Transform::getIdentity(), global_pose.pose); geometry_msgs::PoseStamped robot_pose; tf2::toMsg(tf2::Transform::getIdentity(), robot_pose.pose); robot_pose.header.frame_id = robot_base_frame_; robot_pose.header.stamp = ros::Time(); // latest available ros::Time current_time = ros::Time::now(); // save time for checking tf delay later // get robot pose on the given costmap frame try { tf_.transform(robot_pose, global_pose, costmap->getGlobalFrameID()); } catch (tf2::LookupException& ex) { ROS_ERROR_THROTTLE(1.0, "No Transform available Error looking up robot pose: %s\n", ex.what()); return false; } catch (tf2::ConnectivityException& ex) { ROS_ERROR_THROTTLE(1.0, "Connectivity Error looking up robot pose: %s\n", ex.what()); return false; } catch (tf2::ExtrapolationException& ex) { ROS_ERROR_THROTTLE(1.0, "Extrapolation Error looking up robot pose: %s\n", ex.what()); return false; } // check if global_pose time stamp is within costmap transform tolerance if (current_time.toSec() - global_pose.header.stamp.toSec() > costmap->getTransformTolerance()) { ROS_WARN_THROTTLE(1.0, "Transform timeout for %s. " \ "Current time: %.4f, pose stamp: %.4f, tolerance: %.4f", costmap->getName().c_str(), current_time.toSec(), global_pose.header.stamp.toSec(), costmap->getTransformTolerance()); return false; } return true; }

// Function to get the robot pose in the given costmap frame
bool MoveBase::getRobotPose(geometry_msgs::PoseStamped& global_pose, costmap_2d::Costmap2DROS* costmap) {
// Set the global pose to the identity transform
tf2::toMsg(tf2::Transform::getIdentity(), global_pose.pose);
// Create a new pose for the robot and set it to the identity transform
geometry_msgs::PoseStamped robot_pose;
tf2::toMsg(tf2::Transform::getIdentity(), robot_pose.pose);
// Set the frame ID for the robot pose to the robot base frame
robot_pose.header.frame_id = robot_base_frame_;
// Set the time stamp for the robot pose to the latest available time
robot_pose.header.stamp = ros::Time(); // latest available
// Save the current time for checking the tf delay later
ros::Time current_time = ros::Time::now(); // save time for checking tf delay later

// Get the robot pose on the given costmap frame
try
{
tf_.transform(robot_pose, global_pose, costmap->getGlobalFrameID());
}
catch (tf2::LookupException& ex)
{
// If the transform lookup fails, print an error message and return false
ROS_ERROR_THROTTLE(1.0, "No Transform available Error looking up robot pose: %s\n", ex.what());
return false;
}
catch (tf2::ConnectivityException& ex)
{
// If there is a connectivity error, print an error message and return false
ROS_ERROR_THROTTLE(1.0, "Connectivity Error looking up robot pose: %s\n", ex.what());
return false;
}
catch (tf2::ExtrapolationException& ex)
{
// If there is an extrapolation error, print an error message and return false
ROS_ERROR_THROTTLE(1.0, "Extrapolation Error looking up robot pose: %s\n", ex.what());
return false;
}

// Check if the time stamp of the global pose is within the costmap transform tolerance
if (current_time.toSec() - global_pose.header.stamp.toSec() > costmap->getTransformTolerance())
{
// If the time stamp is outside the tolerance, print a warning and return false
ROS_WARN_THROTTLE(1.0, "Transform timeout for %s. " \
"Current time: %.4f, pose stamp: %.4f, tolerance: %.4f", costmap->getName().c_str(),
current_time.toSec(), global_pose.header.stamp.toSec(), costmap->getTransformTolerance());
return false;
}

// Return true if the robot pose was successfully retrieved
return true;
}