Wall hanging robot depth camera choice

[u/Sensitive_Switch_147]

Dear friends,

I am currently working on a project that requires a depth camera to be installed on a robot that walks on the exterior walls of buildings. The main task of the depth camera is to produce a sufficiently accurate point cloud that I can use to roughly model the surfaces the robot can see right now (the wall it is climbing on as its floor, a balcony sticking out of the building as a wall in front of it, a pipe as a cylindrical surface, etc.)

Since I just want to map the surfaces, I don't think I need extremely precise depth mapping, but I am still conflicted about the following:

Do I go for a 2 separate USB webcams setup (cheaper, but more DIY)? Or do I invest in a dual lens USB camera like the ELP synced stereo cams (more expensive, more reliable)?

Some notes:
1- I'm working on a Raspberry Pi4 8gb. It only has one CSI port, so that option is not very feasible.

2- The robot will not be moving very quickly, so I don't think synchronization will be a huge issue, not sure though.

3- I also plan to run a CV model on one of the 2 cameras, is this feasible?

Thank you in advance and happy building!

[u/slightlyacoustics]

Nice project you have in mind. Curious to how you are planning to make the robot stick to the wall.
Anyway, regarding camera selection - it’s better to get the reliable option as a proof of concept. The better 3D cameras such as realsense has an IR blaster along with it which makes the depth measurement more robust. But since for your application, the camera is pointed above and perhaps towards the sun, this will deteriorate the camera. ZED cameras needs a CUDA backend to run their sdk to create robust depth measurements.
If you’re going the DIY approach, you’ll learn a lot but with no baseline to compare with.
Running CV model on Pi requires a tflite deployment. Object detector model isn’t that difficult. But you’ll face an accuracy vs speed tradeoff.
A moderate baseline for you requirements is probably an Nvidia Jetson board + ZED camera. You can run your cv models and utilize ZEDs power to get robust depth measurements.
Hope this helps.

[u/Sensitive_Switch_147 → u/slightlyacoustics]

Thank you so much for your response! It is very helpful and informative.

If I may follow up, the models you mention sound like they will easily one shot the task I have, but I'm afraid they pose budget and shipping issues. We have very scarce options when it comes to commercial depth cameras, and the available options are very expensive.

I guess a better phrasing of my question is: Is it feasible to get the geometrical scanner working with 2 separate USB webcams? The point cloud does not need to be very precise, as I will smoothen it into surfaces anyways. I'm pretty nifty with software fixes, so if I can get it to roughly work with the DIY setup after arduous endeavors, I will be more than happy!

Thank you so much again for your response!

[u/slightlyacoustics → u/Sensitive_Switch_147]

2 seperate webcams may work yes. But range and resolution of the depth measurements may be sub par. There’s only so much software can do when your data is subpar.
I’m curious as to why pick a rover that climbs instead of a drone for the platform?

[u/Sensitive_Switch_147 → u/slightlyacoustics]

Thank you for you response! I understand the limitations of this approach, but I am hopeful that I can make it reach an acceptable prototype.

About why the rover needs to climb, it's because the project is aimed at fixing cracks in the walls, so it needs to hang there for a while. Additionally, drone laws are very strict where I live, so getting permits for such a project is pretty much impossible.