gravity online estimation

[giangdao1402]

Hey, @peterWon
Thank for your interesting work !
I see that you adopt gravity factor from cartographer 3D, i have read the paper as well as the code. I have tested some SOTA framework with gravity factor and without gravity factor, and the output odometry is better with gravity factor. But I can not figure out what exactly gravity factor affect odometry, what is the true purpose of it . If you have time please give me some answers.
This problem bother me for a week.
Thanks

[peterWon]

Hi, @giangdao1402 , the gravity factor serves as a prior constraint in our front-end. We add this term to make sure the built submap is gravity-aligned so that we can project it to the 2D plane and construct loop constraints from the 2D submaps. You can regard the online estimation of gravity just as a repeat of initialization except that the velocity, pose, and biases are known at this time.

[giangdao1402]

Thank you @peterWon
So if i just simple estimate gravity online (without project ...) and add it to graph of my LIO system, it still benefits pose compare to constant gravity pre-defined, right ?