ar_pose+ceiling camera+calibration file

edit

Hello,

I have a ceiling camera that publishes images in the topic "/camera/image_raw" (working and publishing perfectly through the network). I have also calibrated this camera using openCV calibration procedures and saved this calibration in a .yaml file. I am trying to use ar_pose_multi to get the data published in /ar_pose_marker. When I run:

roslaunch ar_pose ar_pose_multi.launch

it opens rviz simulator and there is the following error:

ERROR: cannot launch node of type [usb_cam/usb_cam_node]: usb_cam

I ignored this error because I dont have usb_cam...I get my images from the ceiling camera (but I dont know if I can ignore this). Finally, I printed a pattern present in /ccny_vision/ar_pose/data/4x4/ and put bellow the camera and I have tried different heights and distances from the camera.

My questions are:

1) I dont want to use the calibration procedure from ROS... Is it possible to use the .yaml calibration file that I already have to feed the topic /camera/camera_info, required by ar_pose_multi?

2) I used rostopic echo with /camera/image_raw and /camera/camera_info and there are data (although calibration has the majority of data without any values), but when I used rostopic echo with /ar_pose_marker there is no output. Do you have any idea about how ar_pose publishes in /ar_pose_marker?

3) Rviz opens normally, but it seems to be completely detached from the camera, so nothing appears on the screen.

I dont know if I have no output because my marker is too small, or my calibration file is wrong, or the usb_cam error is relevant.. I am a little lost :(

================ BEGIN EDIT: Adding more information that can be helpful:

1) I calibrated again the camera using the calibration procedure from ROS and now the calibration is successfully published in "camera/camera_info" topic.

2) the topic "/camera/image_raw" is also OK and I can see the image if I add the component "Image" to Rviz. However with the component "Camera" I have a warning "No Image received"

3) No error is triggered when I run the ar_pose_multi.launch node. But even so, when I put a marker below the camera, nothing happens, no marker seems to be tracked. Also, the topic "/ar_pose_makers" does not presents any value to me.

================ END EDIT

================ BEGIN EDIT: (2)

maybe it is helpful: I am using ROS indigo and Ubuntu 14.04

my ar_pose_multi-launch is:

<launch>
    <node pkg="rviz" type="rviz" name="rviz"/>
        args="-d $(find ar_pose)/launch/live_single.vcg"/>
    <node pkg="tf" type="static_transform_publisher" name="world_to_cam" 
        args="0 0 0.5 -1.57 0 -1.57 world usb_cam 1" />
    <node name="ar_pose" pkg="ar_pose" type="ar_multi" respawn="false" output="screen">
        <param name="marker_pattern_list" type="string" value="$(find ar_pose)/data/object_4x4"/>
        <param name="threshold" type="int" value="100"/>
    </node>
</launch>

The output of rostopic for /camera/camera_info is:

---
header: 
  seq: 131827
  stamp: 
    secs: 1422538316
    nsecs: 930701784
  frame_id: /camera
height: 1920
width: 2560
distortion_model: plumb_bob
D: [-0.477363, 0.142675, 0.003122, -0.00082, 0.0]
K: [1294.855301, 0.0 ...