Show markers in rviz above laserscan

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Hello guys,

I have a task and don't know if I am on the right track, here is first of all my setup/preparation:

I am using the Intel Realsense D435 depth camera and get aligned (i.e. same coordinate system for both lenses) RGB and depth data. I converted the depth image with the depthimage_to_laserscan package to a laser scan (and can display it in rviz, everything fine). Furthermore, I run the dnn_detect package for object detection and can read/extract the bounding boxes from the RGB image.

What I want to do is:

In rviz, display markers above my laserscan which corresponds to the detected objects.

Simple example:

I detected a person in pixels x (100-300) and a cat in pixels x (400-500) in my RGB image. Above every laserscan ray (lets say 2 meters above) which has the x coordinate 100-300, I wanna place green markers (for person), above every laserscan ray which has the x coordinate 400-500, I wanna place blue markers (for cat). In that case, I can visualize the distances through the laserscan and somehow display the detected objects through the colored markers above the scan.

But I stuck at the implementation. Should I write a single node, where I subscribe to the laserscan topic (to get the coordinates of the rays) and to the dnn_objects topic (to get the x coordinates of the detected objects) and publish a MarkerArray message? Or should I separate all and write 3 single nodes? If the former, how can I guarantee the correct timing? Or is it maybe way easier than I think to accomplish my problem?

I would be thankful for every advice.

Ubuntu 16.04 LTS with ROS kinetic and rospy