bounding box PTR input

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Hello everyone, I'm working on object tracking and I'm trying to apply euclidian cluster extraction and then fit bounding boxes around the clusters, before tracking them.

The problem I'm facing is, that my base-code is based on nodelets etc. and not as straightforward as in the tutorials provided by PCL.

Right now I'm struggling to get the bounding boxes around the clusters. For the cluster extraction I used the samples from the perception_pcl on github ( I didn't alter the code) Github link to Code I'm using

And it's working with my input PointCloud. For the bounding boxes I found this function:

visualization_msgs::Marker mark_cluster(pcl::PointCloud<pcl::PointXYZRGB>::Ptr cloud_cluster, std::string ns ,int id, float r, float g, float b)
{
  Eigen::Vector4f centroid;
  Eigen::Vector4f min;
  Eigen::Vector4f max;

  pcl::compute3DCentroid (*cloud_cluster, centroid);
  pcl::getMinMax3D (*cloud_cluster, min, max);

  uint32_t shape = visualization_msgs::Marker::CUBE;
  visualization_msgs::Marker marker;
  marker.header.frame_id = cloud_cluster->header.frame_id;
  marker.header.stamp = ros::Time::now();

  marker.ns = ns;
  marker.id = id;
  marker.type = shape;
  marker.action = visualization_msgs::Marker::ADD;

  marker.pose.position.x = centroid[0];
  marker.pose.position.y = centroid[1];
  marker.pose.position.z = centroid[2];
  marker.pose.orientation.x = 0.0;
  marker.pose.orientation.y = 0.0;
  marker.pose.orientation.z = 0.0;
  marker.pose.orientation.w = 1.0;

  marker.scale.x = (max[0]-min[0]);
  marker.scale.y = (max[1]-min[1]);
  marker.scale.z = (max[2]-min[2]);

  if (marker.scale.x ==0)
      marker.scale.x=0.1;

  if (marker.scale.y ==0)
    marker.scale.y=0.1;

  if (marker.scale.z ==0)
    marker.scale.z=0.1;

  marker.color.r = r;
  marker.color.g = g;
  marker.color.b = b;
  marker.color.a = 0.5;

  marker.lifetime = ros::Duration();
//   marker.lifetime = ros::Duration(0.5);
  return marker;
}

Now my problem is, I don't know what Input I need as Ptr for this function. If I use "output", which is the output of the cluster in the cpp file, I gives me this error message:

catkin_ws/src/perception_pcl/pcl_ros/src/pcl_ros/segmentation/extract_clusters.cpp:375:29: error: could not convert ‘output’ from ‘pcl_ros::PCLNodelet::PointCloud {aka pcl::PointCloud<pcl::PointXYZ>}’ to ‘pcl::PointCloud<pcl::PointXYZRGB>::Ptr {aka boost::shared_ptr<pcl::PointCloud<pcl::PointXYZRGB> >}’
       mark_cluster(output, i);

I would appreciate any help and thank you in advance! I have very limited experience with cpp, so I'm guessing the solution should be rather obvious.