Question

我正在从Leap Motion传感器读取手势，我想计算手在derivativex = dx / dt方向上移动的速度（通过计算X）。我的解决方案是将100个手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，用新值不断更新此数组。

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

我做错了什么？ link代表我的回调正在监听的主题。

我的回叫功能：

#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;  
       }
    }

Answer 1

问题1：日志函数ROS_ERROR被滥用。您应该传递浮点数而不是字符串，否则，您将得到未定义的行为：

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

问题2：由于for循环开始时的赋值，X的导数始终为0：

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 
       }
}

我猜您想将msg-> palmpos.x附加到vectorx吗？您应该为vectorx使用std :: vector，它会容易得多。

这是使用std :: vector的程序的修改版本：

//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

将来自一个主题的数据放入回调函数中的动态数组中并进行一些计算

1 个答案: