Mike, while the tutorial for setting up the navigation stack says that you can just set the static_map: yaml setting to false if you don't have a map server, I have found it easier to just setup a map server and give it a small white image, basically just a blank map.
Okay, cool. I added a small note to the global_costmap section of the wikipage clarifying this.
For the moment, I'll try just using false; if that doesn't work out, I'll experiment with a blank map.
You can also set all costmaps to rolling windows with their global
frame as /odom. As long as you actually publish a tf between that and
base_link (or whatever you want to call your equivalent frames), you
should be able to run completely without a map server. I can
definitely say that it is possible to run navigation without a static
map - I am currently doing just that and have had no issues related to
lack of map server.
Okay, cool. For the moment, my preference would be to avoid map_server. Our initial ROS deployment is for a lightweight open-water craft, so it's unnecessary.
As far as required transforms goes, you really ought to be publishing
transforms for the different frames. You could use the
static_transform_publisher node to publish a static transform, but the
transform from base_link to odom is not static, so you will need to
broadcast that transform yourself.Another option is to use one of the
existing simulators (stage and gazebo) that hook into ROS, which
broadcast all the transforms you should need.
The documentation I've been following for this process is at navigation/Tutorials/RobotSetup/TF, which just speaks about setting up a transform between base_link and a sub-part (laser scanner). Is there somewhere else I need to be looking for information about the base_link -> odom and base_link -> map transforms? What do these transforms represent, and what's the relationship between them and the information that's already in my odom topic?
If I make the base_link not be on-board the robot, are there ways that it's going to bite me later if/when I do end up adding a map, or if I'm trying to set up a multi-robot system?
Sorry for the barrage of questions, but I really appreciate your assistance. I'm trying to do my best document things as I discover them, to help out future newbies.
Mike