when applying the dual ekf, from what I understand, you get two odometries, the local and the global, I would like to ask you what are the differences between the two.
I don't know specifically what is being done on a Jackal, but I can give a general answer:
"global localization" refers to an algorithm that directly calculates an absolute pose on the map. A GPS sensor can be an input to this calculation. The downside is that typically it takes a long time (i.e. seconds) to get an update; for us, GPS has the additional problem that it provides no angle rotation (yaw) information.
"local localization" is different: it relies on measuring relative position changes over time, then integrating them to estimate the current position relative to a starting point. IMU and wheel-encoders are typically the input for this. Pose updates can happen very quick (milliseconds), but the downside is that (a) it has to be told the robot's starting pose on a map, and (b) measurement errors accumulate over time, so the output "drifts" (becomes inaccurate.)
What people do is combine both methods: use local localization to continuously track a decent estimate of the robot pose, and "occasionally" correct the drift using global localization.
The "local ekf" is almost certainly fusing IMU odometry and wheel-encoder odometry.
The "global ekf" is probably applying a velocity-based prediction model to the GPS sensor data.
what role that the navsat transform have in practice in the robot localization
You have to convert from the spherical longitude/latitude coordinate system to your robot's flat 2d map coordinate system.
I think your question is too broad, and I doubt anyone here has the time to debug your project for you. If you have a specific ros question about gps or ekf or move_base, or have a specific ros error message you would like explained, we can try to help you with that.
Thank you for the answer, i see that is too broad, so my questions are the follows. 1) when applying the dual ekf, from what I understand, you get two odometries, the local and the global, I would like to ask you what are the differences between the two. 2) The other question is that, from what I understand the navsat tranform takes as input the local odometry of the ekf gave as output, I would like to ask you why it takes the global. 3) furthermore what role that the navsat transform have in practice in the robot localization