How to close a loop with a tilted camera?

[udaykiran2021]

Hello,

Thanks for your great effort.

I have a question.
Is there a way that we can give rgbd camera extrinsic parameters as input to openvslam? Ex: camera angle.
If yes, could you please specify which source file needs to be modified?

Problem faced:
When the camera is tilted downward with an angle, the localization result is not good.

[ymd-stella]

rgbd camera

What camera are you using?

When the camera is tilted downward with an angle, the localization result is not good.

If it doesn't work fine, the first thing to do is to investigate the cause. We should not complicate the problem by adding new factors.
Can you provide config file and video input/output of OpenVSLAM?

[ymd-stella]

I don't know how many degrees you are tilting the camera, but are you tilting the camera so far that no horizontal landmarks are visible?
In such a situation, matching between keyframes over long distances will not work, so it is not surprising that performance degrades.

Why do you want to tilt the camera?

[udaykiran2021]

RealSense is used for OpenVSLAM and Freespace detection, and Freespace should face downward as much as possible (about 1m away from feet)

Tilt angle = around 15deg.
I understand that fewer landmarks will result in less accuracy with tilted camera, but my problem is that I want to eliminate the height gap in z-axis when the camera is tilted.
I would like to reduce the z axis gap between start and end point which is same in my case.

[ymd-stella]

First, I recommend that you prepare one camera for localization and one for free space detection. In general, the camera for free space detection needs to be placed so that nearby objects are visible, while the camera for localization needs to be placed so that nearby objects are not visible. This means that the camera for localization should be placed higher.

Next, in a forced and practical way, place a landmark on the ground at the starting point. If OpenVSLAM can detect the loop, the loop closure can close the loop.

Or, although it may be difficult. Think about a way to increase the field of view. The field of view of the D455 is a little too narrow to be used for Visual SLAM. You might be able to stitch together images from multiple cameras and input them as an equirectangular format image.

[udaykiran2021]

Thank you so much for your suggestion. Let me discuss this and will get back.

[udaykiran2021]

Next, in a forced and practical way, place a landmark on the ground at the starting point. If OpenVSLAM can detect the loop, the loop closure can close the loop.

We decided to go ahead with this suggestion and check if there is any improvement.