could not find camera topic on rviz - ros

Question

I was launching the techman robot on ros using the demo.launch. The first time when I launched it on rviz I could able to see the camera under by topic and I can see the video output. So I edited the moveit setup and added some poses to the robot. so when I launched again. now I could not find a camera under by topic. And I am very new to ros.
and the following was my demo.launch file
<launch>
<!-- specify the planning pipeline -->
<arg name="pipeline" default="ompl" />
<!-- By default, we do not start a database (it can be large) -->
<arg name="db" default="false" />
<!-- Allow user to specify database location -->
<arg name="db_path" default="$(find new_techman)/default_warehouse_mongo_db" />
<!-- By default, we are not in debug mode -->
<arg name="debug" default="false" />
<!-- By default, we will load or override the robot_description -->
<arg name="load_robot_description" default="true"/>
<!-- Set execution mode for fake execution controllers -->
<arg name="execution_type" default="interpolate" />
<!--
By default, hide joint_state_publisher's GUI
MoveIt!'s "demo" mode replaces the real robot driver with the joint_state_publisher.
The latter one maintains and publishes the current joint configuration of the simulated robot.
It also provides a GUI to move the simulated robot around "manually".
This corresponds to moving around the real robot without the use of MoveIt.
-->
<arg name="use_gui" default="false" />
<arg name="use_rviz" default="true" />
<!-- If needed, broadcast static tf for robot root -->
<!-- We do not have a robot connected, so publish fake joint states -->
<node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" unless="$(arg use_gui)">
<rosparam param="source_list">[move_group/fake_controller_joint_states]</rosparam>
</node>
<node name="joint_state_publisher" pkg="joint_state_publisher_gui" type="joint_state_publisher_gui" if="$(arg use_gui)">
<rosparam param="source_list">[move_group/fake_controller_joint_states]</rosparam>
</node>
<!-- Given the published joint states, publish tf for the robot links -->
<node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher" respawn="true" output="screen" />
<!-- Run the main MoveIt! executable without trajectory execution (we do not have controllers configured by default) -->
<include file="$(find new_techman)/launch/move_group.launch">
<arg name="allow_trajectory_execution" value="true"/>
<arg name="fake_execution" value="true"/>
<arg name="execution_type" value="$(arg execution_type)"/>
<arg name="info" value="true"/>
<arg name="debug" value="$(arg debug)"/>
<arg name="pipeline" value="$(arg pipeline)"/>
<arg name="load_robot_description" value="$(arg load_robot_description)"/>
</include>
<!-- Run Rviz and load the default config to see the state of the move_group node -->
<include file="$(find new_techman)/launch/moveit_rviz.launch" if="$(arg use_rviz)">
<arg name="rviz_config" value="$(find new_techman)/launch/moveit.rviz"/>
<arg name="debug" value="$(arg debug)"/>
</include>
<!-- If database loading was enabled, start mongodb as well -->
<include file="$(find new_techman)/launch/default_warehouse_db.launch" if="$(arg db)">
<arg name="moveit_warehouse_database_path" value="$(arg db_path)"/>
</include>
</launch>
and when I launch the gazebo.launch that was created by the moveit setup assistant I can see the camera from the gazebo platform into rviz

Answer 1

Have you launched Gazebo before or after launching your demo.launch? Try doing it the other way around!
It seems that Gazebo provides your camera-simulation. Rviz itself doesn't create the camera view, it just listens to a topic where a different engine (normally a robot, in your case the robot-simulation of Gazebo) publishes the images and then shows these images to you.
Rviz and Gazebo sometimes have trouble communicating based on which is started first.