How to implement bumper pointcloud on a custom robot?

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Take a look at this implementation of a "virtual bumper" that does essentially what you want, but by using comparison of the odometry and pose data to detect collisions (no bump sensors needed!).

The key part of the code that populates the pointcloud is:

  // place obstacle into point cloud 0.25 meters in front of robot
  float val = 0.25;
  memcpy(&pointcloud_.data[0 * pointcloud_.point_step + pointcloud_.fields[0].offset], &val, sizeof(float));
  val = 0.0;
  memcpy(&pointcloud_.data[0 * pointcloud_.point_step + pointcloud_.fields[1].offset], &val, sizeof(float));

  pointcloud_.header.stamp = ros::Time::now();
  pointcloud_pub_.publish(pointcloud_);

  collision_pub_.publish(true);

In the above, an obstacle is placed 0.25 meters in front of the robot (when a collision occurs), and with a Y translation of zero. Note: if you have left and right bumpers, you would add +/-Y numbers for that instead of zero.

To get it to work with gmapping, you could try converting the pointcloud into a laserscan and then publish that (on the same topic as the regular scan). There are tools for this conversion such as http://wiki.ros.org/pointcloud_to_laserscan

Here's the full implementation of the virtual bumper. It's a working standalone node that you could run without modification. It assumes you have pose and odometry data from somewhere. This was tested with the navigation stack and worked fine when used to populate the costmap obstacle layer.

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#include "ros/ros.h"
#include "nav_msgs/Odometry.h"
#include "geometry_msgs/Twist.h"
#include "geometry_msgs/PoseWithCovarianceStamped.h"
#include "tf/tf.h"
#include "std_msgs/Bool.h"
#include "sensor_msgs/PointCloud2.h"

class VirtualBumper
{
  public:
    VirtualBumper();
    virtual ~VirtualBumper() {};

  protected:
    void odomCallback ...