Re: [BRH-list] NAV2 SLAM

[Pito Salas]

David— this is from another thread where I explain what I’ve learned so far about slam_toolbox and the error that you and I were discussing.

Ken--

Thanks. I have goten a few responses but in each case I was already past the point. So voila, I think I’m the expert now.

I’ve made progress on this. Here is current theory of the case:

- there are two formats for maps. The traditional one as generated and used by nav2 consist of two files, .yaml+.pgm. The new kind as generated by slam_toolbox consists of two files: .posegraph+.data. Lets call them tradmap and newmap.

- the path in the yaml file is on;y used when slam_toolbox starts up to pick up where it left off last time. It is looking for a “new-map” and if it finds it then it loads it up and through math magic figures out where to continue building the map

- nav2 does not understand newpaps so it cant use them for path planning or amcl

- slam_toolbox understands both kinds of maps and builds both of them

- slam toolbox is building both kinds of maps simultaneously because you need a tradmap to do navigation. Slam_toolbox does not know about navigation

- the error about the starting location is spurious and occurs whenever slam_toolbox does not find a map

I will continue on this quest and plan to write up something at the end and ask Steve Macenski to verify my reverse engineering experimentation!

Pito

> On Oct 17, 2025, at 1:10 PM, Ken Gregson <ken.g...@gmail.com> wrote:
>
> Pito,
>
> (Here's a trivial message ;-)
>
> Did you get any responses to help with the missing "basement" pose graph file?
>
> I'll assume not and ask if that file already exists, how you made it, and what format it is in?
>
> Could be as simple as using the fully qualified path to it in the map_file_name parameter?
>
> It may need to already exist and you can "cause" one to be created by running without one first, and forcing it to be saved in order to "resume".
> https://answers.ros.org/question/361187/
>
> Haven't used this in a while (but am about to with the makers pet) so just a shot in the dark.
>
> -Ken
>
> --
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Best,

Pito

Boston Robot Hackers &&
Comp. Sci Faculty, Brandeis University (Emeritus)