What triggers an update to IMU bias linearization point?

[Mike]

My understanding is IMU pre integration term uses a fixed linearization point for the bias and to update it requires recomputing the pre entire pre integration interval.

What triggers when that computation is done?

[Dellaert, Frank]

Ah, no. The whole point of the IMU factor is to avoid the recomputing: Once the PIM is created from the IMU measurements it is immutable. What's happening here instead is we also compute a Jacobian of the bias change on the result. So, when the bias estimate changes, we're computing the delta in the IMU factor and update the residual based on that. 

Practical advice: do use the best possible estimate of the bias you have, not just zero.   So, as your bias estimate evolves over time, give that to the PIM in the constructor. 

Best

Frank

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[Mike]

Hi Frank,

To make sure I understand, you are saying the linearization point of the bias estimation after the PIM factor is created never changes? Is there any way to force it to update after some criteria? Or would that come down to basically cycling through the graph and creating new factors?

Thanks

[Dellaert, Frank]

That’s correct. And that would be a drastic intervention with questionable payoff. But, if you can show that some applications the payoff is large, I’d love to know about it :-)

Best!

Frank

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From: gtsam...@googlegroups.com <gtsam...@googlegroups.com> on behalf of Mike <lowel...@gmail.com>

Sent: Friday, 19 June 2026 16:05:53
To: gtsam users <gtsam...@googlegroups.com>
Subject: Re: [GTSAM] What triggers an update to IMU bias linearization point?

 

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