Usage format of depth_image_proc/point_cloud_xyzrgb

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I intend to extract point cloud of some objects in pybullet simulation environment. My intension is to record depth and rgb images of those objects by using built-in functions of pybullet environment. Then, by using those images, I want to produce point clouds of those images. To accomplish this, I think that I can use point_cloud_xyzrgb nodelet of depth_image_proc package.

The problem is that I have used services, nodes, publishers and subscribers, but I have no experience about nodelets and how to use them at all. Hence, I do not know how I can do that by using this nodelet.

Is there anyone who can explain the usage format of nodelets ?