Simple obstacle distance calculation

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I'm pretty new to ROS and I need to implement basic obstacle detection using PointCloud2 data.

My idea was to just check distance to a closest obstacle in front of the robot and send the message to stop moving if it is too close (I don't want to go around it). I thought about removing the floor from the point cloud and just checking distance to a closest points.

I tried to find solution on the internet as it seemed to be pretty easy task but I'm really struggling to find anything. Closest thread to what I want was this: https://answers.ros.org/question/3205... But only answer said it is "pretty generic task" and to check tutorials: http://wiki.ros.org/pcl/Tutorials. Which isn't helpful really.

I've read that tutorial and I have basic code working but now I'm stuck and I have no idea how to progress further. Other tutorials honestly are too hard and complex for me right now and just go over my head. I only need to accomplish one of the simplest task imaginable, without creating maps and planing the paths. Please help.

Ubuntu 18.04 with Ros Melodic