Question on landmarks and fixedlagsmoother

[Mike]

Hello, 

I am working on implementing a VIO solution with GTSAM as the backend, one question I have is how landmark time-stamping and removal would be handled. If I could manually marginalize out landmarks based upon a key that would be easiest but it doesn't look like I can do that - is marginalization strictly time based?

From my understanding, I will need to use the KeyTimestampMap argument to tie landmarks into image timestamps - is this right? From some browsing it appears that when a landmark shows up in the most recent image, I update the landmark timestamp to the image timestamp. This keeps the landmark fresh so the fixed lag smoother won't remove it automatically - is this the correct approach? 

- Michael

[Dellaert, Frank]

Hi Michael

The FixedLagSmoother is really a thin class that implements a strictly time-based marginalization strategy. It has an internal data structure,  mapping measurements to time-stamps. I would not recommend trying to hack that system, but rather -if you need a different marginalization strategy- writing your own class. Read the source code, it's not really that hard :-)

Best

FD

From: gtsam...@googlegroups.com <gtsam...@googlegroups.com> on behalf of Mike <lowel...@gmail.com>
Date: Monday, December 1, 2025 at 8:49 PM
To: gtsam users <gtsam...@googlegroups.com>
Subject: [GTSAM] Question on landmarks and fixedlagsmoother

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