libviso2 empty topics

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I am using the viso2_ros package, which provides the ros wrappers for the Visual Odometry package libviso2, to track a moving monocular camera. For this purpose I am using the Asus Xtion Pro which directly generates both mono and rgb image topics. Then I am also running the image_proc node to rectify those images. After that I am running the mono_odometer node of the viso2_ros package. However the viso2_ros doesn't seem to be publishing any values. The "rostopic list" gives the pose and odometry topics, however echoing them shows nothing, indicating the topics are empty. I cannot figure out why ? Can anyone help me point out where the problem lies?