robot_localization: "Global EKF" without absolute pose information

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Hello there,

I am attempting the obtain accurate pose information from my "global ekf" (with map -> odom transform) in the event that my lidar stops functioning, which results in AMCL to stop publishing pose updates.

To give some context, I have two r_l nodes running. The first in "local mode" (odom -> base_link) and the second in "global mode" (map -> odom). My local EKF is providing me with splendid results (approximate error of <1m after travelling for 200m). Because of this, I do not see any reason why I would not be able to obtain similar results for the global EKF by using the same parameters. However, this is not the case. I have tried to run two instances of the r_l node with the exact same parameters, except for a difference in the world_frame parameter.

The configuration that I use for both EKFs are as follows:

frequency: 25
sensor_timeout: 0.1
two_d_mode: true
transform_time_offset: 0.0
transform_timeout: 0.0

print_diagnostics: true
debug: false
debug_out_file: /path/to/debug/file.txt

publish_tf: true
publish_acceleration: false

map_frame: map              # Defaults to "map" if unspecified
odom_frame: odom            # Defaults to "odom" if unspecified
base_link_frame: base_footprint  # Defaults to "base_link" if unspecified
world_frame: odom or map           # Defaults to the value of odom_frame if unspecified

odom0: /odom
odom0_config: [false,  false,  false,
               false, false, false,
               true, true, false,
               false, false, true,
               false, false, false]
odom0_queue_size: 2
odom0_nodelay: false
odom0_differential: false
odom0_relative: false

imu0: /imu
imu0_config: [false, false, false,
              false, false, false,
              false, false, false,
              false, false, true,
              false, false, false]
imu0_nodelay: false
imu0_differential: false
imu0_relative: true
imu0_queue_size: 5
imu0_remove_gravitational_acceleration: false

use_control: false
stamped_control: false
control_timeout: 0.2
control_config: [true, false, false, false, false, true]
acceleration_limits: [2.6, 0.0, 0.0, 0.0, 0.0, 6.8]
deceleration_limits: [2.6, 0.0, 0.0, 0.0, 0.0, 6.8]
acceleration_gains: [0.8, 0.0, 0.0, 0.0, 0.0, 0.9]
deceleration_gains: [1.0, 0.0, 0.0, 0.0, 0.0, 1.0]

process_noise_covariance: 
  [0.05, 0,    0,    0,    0,    0,    0,     0,     0,    0,    0,    0,    0,    0,    0,
   0,    0.05, 0,    0,    0,    0,    0,     0,     0,    0,    0,    0,    0,    0,    0,
   0,    0,    0.01, 0,    0,    0,    0,     0,     0,    0,    0,    0,    0,    0,    0,
   0,    0,    0,    0.03, 0,    0,    0,     0,     0,    0,    0,    0,    0,    0,    0,
   0,    0,    0,    0,    0.03, 0,    0,     0,     0,    0,    0,    0,    0,    0,    0,
   0,    0,    0,    0,    0,    0.80, 0,     0,     0,    0,    0,    0,    0,    0,    0,
   0,    0,    0,    0,    0,    0,    0.550, 0,     0,    0,    0,    0,    0,    0,    0,
   0,    0,    0,    0,    0,    0,    0,     0.001, 0,    0,    0,    0,    0,    0,    0,
   0,    0,    0,    0,    0,    0,    0,     0,     0.01, 0,    0,    0,    0,    0,    0,
   0,    0,    0,    0,    0,    0,    0,     0,     0,    0.01, 0,    0,    0,    0,    0,
   0,    0,    0,    0,    0,    0,    0,     0,     0,    0,    0.01, 0 ...