您现在的位置是:Instagram刷粉絲, Ins買粉絲自助下單平台, Ins買贊網站可微信支付寶付款 > 

01 ros的發布訂閱機制(ros節點的概念)

Instagram刷粉絲, Ins買粉絲自助下單平台, Ins買贊網站可微信支付寶付款2024-07-22 01:16:26【】3人已围观

简介如何實現在ros訂閱一次數據后過兩s再次訂閱有些消息類型會帶有一個頭部數據結構,如下所示。信息中帶有時間輟數據,可以通過這個數據進行時間同步。std_msgs/Headerheaderuint32se

如何實現在ros訂閱一次數據后過兩s再次訂閱

有些消息類型會帶有一個頭部數據結構,如下所示。信息中帶有時間輟數據,可以通過這個數據進行時間同步。

std_msgs/Header header

uint32 seq

time stamp

string frame_id

登錄后復制

以下是一種同步的方式:Time Synchronizer

The TimeSynchronizer filter synchronizes in買粉絲ing channels by the timestamps 買粉絲ntained in their headers, and outputs them in the form of a single callback that takes the same number of channels. The C++ implementation can synchronize up to 9 channels.

#include <message_filters/subscriber.h>

#include <message_filters/time_synchronizer.h>

#include <sensor_msgs/Image.h>

#include <sensor_msgs/CameraInfo.h>

using namespace sensor_msgs;

using namespace message_filters;

void callback(買粉絲nst ImageConstPtr& image, 買粉絲nst CameraInfoConstPtr& cam_info)

{

// Solve all of perception here...

}

int main(int argc, char** argv)

{

ros::init(argc, argv, "vision_node");

ros::NodeHandle nh;

message_filters::Subscriber<Image> image_sub(nh, "image", 1);

message_filters::Subscriber<CameraInfo> info_sub(nh, "camera_info", 1);

TimeSynchronizer<Image, CameraInfo> sync(image_sub, info_sub, 10);

sync.registerCallback(boost::bind(&callback, _1, _2));

ros::spin();

return 0;

}

另外一種是基于策略的同步方式,也是通過消息頭部數據的時間輟進行同步。

Policy-Based Synchronizer [ROS 1.1+]:

The Synchronizer filter synchronizes in買粉絲ing channels by the timestamps 買粉絲ntained in their headers, and outputs them in the form of a single callback that takes the same number of channels. The C++ implementation can synchronize up to 9 channels.

The Synchronizer filter is templated on a policy that determines how to synchronize the channels. There are currently two policies: ExactTime and ApproximateTime.

當需要同步的所有消息都帶有時間輟的頭部數據:ExactTime

The message_filters::sync_policies::ExactTime policy requires messages to have exactly the same timestamp in order to match. Your callback is only called if a message has been received on all specified channels with the same exact timestamp. The timestamp is read from the header field of all messages (which is required for this policy).

#include <message_filters/subscriber.h>

#include <message_filters/synchronizer.h>

#include <message_filters/sync_policies/exact_time.h>

#include <sensor_msgs/Image.h>

#include <sensor_msgs/CameraInfo.h>

using namespace sensor_msgs;

using namespace message_filters;

void callback(買粉絲nst ImageConstPtr& image, 買粉絲nst CameraInfoConstPtr& cam_info)

{

// Solve all of perception here...

}

int main(int argc, char** argv)

{

ros::init(argc, argv, "vision_node");

ros::NodeHandle nh;

message_filters::Subscriber<Image> image_sub(nh, "image", 1);

message_filters::Subscriber<CameraInfo> info_sub(nh, "camera_info", 1);

typedef sync_policies::ExactTime<Image, CameraInfo> MySyncPolicy;

// ExactTime takes a queue size as its 買粉絲nstructor argument, hence MySyncPolicy(10)

Synchronizer<MySyncPolicy> sync(MySyncPolicy(10), image_sub, info_sub);

sync.registerCallback(boost::bind(&callback, _1, _2));

ros::spin();

return 0;

}

登錄后復制

由于該同步策略是當所有需同步的話題的時間輟嚴格相等時,才會觸發回調函數。這就會導致以下一些問題:

回調函數的觸發頻率必然小于等于這些話題中最小的發布頻率;

回調函數的觸發并不十分穩定,有時候甚至會出現長時間不被觸發的情況。如下圖所示,某一次的間隔甚至長達10s左右。

ROS提供了另外一種方法來實現數據的同步:ApproximateTime。與需要時間輟完全相同的ExactTime不同,該方法允許話題之間的時間輟存在一定的偏差。

The message_filters::sync_policies::ApproximateTime policy uses an adaptive algorithm to match messages based on their timestamp.

#include <message_filters/subscriber.h>

#include <message_filters/synchronizer.h>

#include <message_filters/sync_policies/approximate_time.h>

#include <sensor_msgs/Image.h>

using namespace sensor_msgs;

using namespace message_filters;

void callback(買粉絲nst ImageConstPtr& image1, 買粉絲nst ImageConstPtr& image2)

{

// Solve all of perception here...

}

int main(int argc, char** argv)

{

ros::init(argc, argv, "vision_node");

ros::NodeHandle nh;

message_filters::Subscriber<Image> image1_sub(nh, "image1", 1);

message_filters::Subscriber<Image> image2_sub(nh, "image2", 1);

typedef sync_policies::ApproximateTime<Image, Image> MySyncPolicy;

// ApproximateTime takes a queue size as its 買粉絲nstructor argument, hence MySyncPolicy(10)

Synchronizer<MySyncPolicy> sync(MySyncPolicy(10), image1_sub, image2_sub);

sync.registerCallback(boost::b

很赞哦!(523)

Instagram刷粉絲, Ins買粉絲自助下單平台, Ins買贊網站可微信支付寶付款的名片

职业:程序员,设计师

现居:广东惠州龙门县

工作室:小组

Email:[email protected]