mux nodelets(topic tools)-how to use them ?

edit

i am trying to use the mux_nodelets using the below launch file

   1   <node pkg="nodelet" type="nodelet" name="pcl_manager" args="manager" output="screen" />
   2   <!-- MUX the data onto one topic -->
   3   <node pkg="nodelet" type="nodelet" name="data_mux" args="load pcl/NodeletMUX pcl_manager" output="screen">
   4     <rosparam>
   5       input_topics: [/camera/points, /camera/state]
   6     </rosparam>
   7   </node>

my idea was to mutiplex topics:camera/state and camera/points and read the data_mux output (topic)

but it gives an error as below

Client [/image_converter1] wants topic /data_mux/output to have datatype/md5sum [std_msgs/String/992ce8a1687cec8c8bd883ec73ca41d1], but our version has [sensor_msgs/PointCloud2/1158d486dd51d683ce2f1be655c3c181]. Dropping connection

1. i understand the message type for the mux_nodelet output is PointCloud2 format. how do i change this to a required messsage type ?

2. If i have 2 topics which are having custom message type as input to mux_nodelet. How do i define the the mux_out topic, should i define a message type which is a mix of both the inputs topics ?

PS:the idea of using a nodelet was to save communication time

I am really new to nodelets .Please help .

edit : 16 nov

update : I complied the below code snipped below in one of my header files used in a node

typedef nodelet::NodeletMUX<camera_test::combine, message_filters::Subscriber<camera_test::combine> > NodeletMUX;
PLUGINLIB_DECLARE_CLASS (pcl, NodeletMUX, NodeletMUX, nodelet::Nodelet);

combine is message type defined in the package camera_test (combine message time is a custom message with Header)

but when i run the launch file below and run one addition node which publishes topics /camera/state and /camera/points .

<launch>  
  <node pkg="nodelet" type="nodelet" name="pcl_manager" args="manager" output="screen" />
  <!-- MUX the data onto one topic -->
  <node pkg="nodelet" type="nodelet" name="data_mux" args="load pcl/NodeletMUX pcl_manager" output="screen">
    <rosparam>
      input_topics: [/camera/state, /camera/points]
    </rosparam>
  </node>

</launch>

I get the below warning

[WARN] [1542361466.932969]: Could not process inbound connection: topic types do not match: [sensor_msgs/PointCloud2] vs. [camera_test/combine]{'topic': '/camera/state', 'tcp_nodelay': '0', 'md5sum': '1158d486dd51d683ce2f1be655c3c181', 'type': 'sensor_msgs/PointCloud2', 'callerid': '/pcl_manager'}

it looks like even after calling the PLUGLIB _DECLARE class with new message type,it still expects the message type PointCloud2 ? and if i do a rostopic echo data_mux out ,i get no messages I don`t understand what i am doing wrong .could someone please Help ?

edit 3 : Below is my header file where i have declared the PLUGINLIB_DECLARE class

can you please suggest what i should change here ?

#include <pluginlib/class_list_macros.h>
#include <nodelet/nodelet.h>
#include <nodelet_topic_tools/nodelet_mux.h>
#include <message_filters/subscriber.h>
#include "camera_test/combine.h"
#include <nodelet_topic_tools/nodelet_demux.h>
#include <sensor_msgs/PointCloud2.h>

typedef nodelet::NodeletMUX<camera_test::combine, message_filters::Subscriber<camera_test::combine> > NodeletMUX;
PLUGINLIB_DECLARE_CLASS (pcl, NodeletMUX, NodeletMUX, nodelet::Nodelet);
//typedef nodelet::NodeletDEMUX<sensor_msgs::PointCloud2> NodeletDEMUX;

btw I have not added an plugin.xml file for this nodelet ? could that be the problem ?