Unable to lookup transform, cache is empty.

edit

Hi everybody! I'm a newcomer to the ROS world, so please do correct me when necessary, it will be appreciated. If there's a better way of doing something, I'm also interested and open to corrections. I have searched a lot for questions with similar problems, but none of the solutions work in my case. Now, onto the question:

Edit: I forgot to mention I'm using ROS Fuerte.

I have a Kinect mounted on top of a robot, 16 cm above the robot's referential. What I want to do is to transform the point cloud and depth image that Kinect publishes (in the /camera/depth_registered/points topic) to be referenced to the robot's referential. Also, I want to publish a new point cloud that uses spherical coordinates instead of cartesian coordinates.

Everything seems to be doing what is expected (things appear correct when I see them with Rviz), but after some seconds, the following error message starts to appear repeatedly and everything freezes in Rviz:

Unable to lookup transform, cache is empty, when looking up transform from frame [/camera_rgb_optical_frame] to frame [/impep_frame]

Also, Rviz produces the following warning message:

MessageFilter [target=/impep_frame ]: Discarding message from [/kinectRef2IMPEPRef] due to empty frame_id.  This message will only print once.

This is the launch file I use:

<launch>
  <!-- Launch the static transform publisher that defines the transform
      from IMPEP's referential to Kinect's referential. -->
  <node name="impep_frame_publisher" pkg="tf" type="static_transform_publisher" args="0 0 0.16 0.5 -0.5 0.5 0.5 /impep_frame /camera_link 100" />

  <!-- Launch the node that transforms data from Kinect's referential to
       IMPEP's referential -->
  <node name="kinectRef2IMPEPRef" pkg="IMPEP" type="kinectRef2IMPEPRef" />

  <!-- Include the openni launch file to start the Kinect nodes. -->
  <include file="$(find IMPEP)/launch/openni.launch" />
</launch>

Note: I changed the following line in the openni.launch file to have depth registered output.

<!-- Use OpenNI's factory-calibrated depth->RGB registration? -->
<arg name="depth_registration" default="true" />

This is the code I've written to do all this. I'm aware that some things can be optimized, but I want to understand what's going wrong with this code before I start optimizing it. I put it in Pastebin for easier reading, it is too big to post here (185 lines).

Note: PointDTPRGB is a point type created by myself to contain the spherical coordinates.

Edit2: I just noticed that, after I shutdown the nodes launched by the launch file above, this message related to my problematic node appears:

[kinectRef2IMPEPRef-3] escalating to SIGTERM

If you need any information I might have forgotten, please do ask for it, I will post it as soon as possible. Thanks in advance!