将一个主题中的数据放入 Callback 函数中的动态数组中并进行一些计算

Put data from one topic into a dynamic array in the Callback function and do some calculation

本文关键字：函数 数组 动态 计算 Callback 数据 一个      更新时间：2023-10-16

我正在从Leap Motion传感器读取我的手部姿势，我想计算手在X方向上的移动速度（通过计算derivativex = dx / dt）。我的解决方案是将 100 个手部姿势值放在一个数组中，并在新消息 （ msg->palmpos.x ） 通过主题 leapmotion/data 到达回调函数时不断用新值更新该数组。

我的问题是，当我打印derivativex = dx / dt时，输出始终ROS_ERROR("Hello %f", "derivativex")：0

我做错了什么？我的回调正在侦听的主题的链接。

我的回调函数：

#include "geometry_msgs/TwistStamped.h"
#include "jog_msgs/JogJoint.h"
#include "jog_msgs/leapros.h"
#include "ros/ros.h"
#include <ros/console.h>
#include <iostream>
#include <iomanip>
#include <array>
using namespace std;
namespace to_twist
{
class spaceNavToTwist
{
public:
  spaceNavToTwist() : spinner_(1)

{
    joy_sub_ = n_.subscribe("leapmotion/data", 1, &spaceNavToTwist::joyCallback, this);
    // Changed "spacenav/joy" to topic "/leapmotion/data"
    twist_pub_ = n_.advertise<geometry_msgs::TwistStamped>("jog_arm_server/delta_jog_cmds", 1);
    joint_delta_pub_ = n_.advertise<jog_msgs::JogJoint>("jog_arm_server/joint_delta_jog_cmds", 1);
    spinner_.start();
    ros::waitForShutdown();
  };
  const int arraySize = 100;// constant variable can be used to specify array size
  double vectorx[ arraySize ] = {};// initialize elements of array n to 0
  int resolution = 10;
  double derivativex = 0;
  double dx = 0; 
  int dt = 0;
private:
  ros::NodeHandle n_;
  ros::Subscriber joy_sub_;
  ros::Publisher twist_pub_, joint_delta_pub_;
  ros::AsyncSpinner spinner_;
  // Convert incoming joy commands to TwistStamped commands for jogging.
  void joyCallback(const jog_msgs::leapros::ConstPtr& msg)
 { 
    for ( int count = 0; count < arraySize; ++count ) {// store the values of poses
       vectorx[ count ] = msg->palmpos.x;
       if (count>resolution) {
           dx = vectorx[ count-1 ] - vectorx[ count-(resolution-1) ];
           dt = resolution;
           derivativex = dx / dt;
           ROS_ERROR("Hello %f", derivativex);
       }    
       if (count == arraySize) {
           count=0;  
       }
    }

问题 1：日志函数ROS_ERROR被误用。你应该传递一个浮点数而不是一个字符串，否则，你会得到一个未定义的行为：

       ROS_ERROR("Hello %f", derivativex); // <-- there is no double quotes.

问题 2：X 的导数始终为 0，因为 for 循环开头的赋值：

for ( int count = 0; count < arraySize; ++count ) {// store the values of poses
       //Could you please explain why the program needs this ???
       vectorx[ count ] = msg->palmpos.x; // <-- every element in vectorx is set to this values (const in each function call).
       if (count>resolution) {
           dx = vectorx[ count-1 ] - vectorx[ count-(resolution-1) ]; // is the same as (msg->palmpos.x - msg->palmpos.x) --> 0
           dt = resolution;
           derivativex = dx / dt;
           ROS_ERROR("Hello %f", derivativex);
       }    
       if (count == arraySize) {
           count = 0;  //<-- never get here because of count is always lesser than arraySize 
       }
}

我猜你想将 msg->palmpos.x 附加到矢量 ？你应该使用 std：：vector 来表示 vectorx，它会容易得多。

这是程序的修改版本，使用 std：：vector ：

//add this to your file
#include <vector>
//Your program body ...
//...
//As we are using C++, try to use C++ facilities if possible.
//const int arraySize = 100;// constant variable can be used to specify array size
//double vectorx[ arraySize ] = {};// initialize elements of array n to 0
std::vector<double> vectorx;
int resolution = 10;
int max_vector_size = 100; //keep 100 elements in the vectorx.
//...
// Convert incoming joy commands to TwistStamped commands for jogging.
void joyCallback(const jog_msgs::leapros::ConstPtr& msg)
{ 
     //store the x coordinate in the vectorx
     vectorx.push_back( msg->palmpos.x );
     if( vectorx.size() > resolution ){
         int id_back = vectorx.size() - 1;
         double dx = vectorx[id_back] - vectorx[ id_back - resolution ];
         double dt = resolution;
         derivativex = dx / dt;
         ROS_ERROR("Hello %f", derivativex);
     }
     while(vectorx.size() > max_vector_size ) {
         vectorx.erase( vectorx.begin() ); //remove the first element
     }
}//eof joyCallback
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