Add load / delete ROS services.

[MichaelGrupp]

See also: RFC 29

Signed-off-by: Michael Grupp [email protected]

[MichaelGrupp]

Requires cartographer-project/cartographer#1767 for deleting frozen trajectories. (merged)

[johuber]

why not handle the case and return it with the status?

Should be easy with try / catch rigth?

[johuber]

The load state from file worked as expected.

I got it to crash with the delete call though, following error:
This happened consistently about 15s after the call to the delete service (of a FINISHED trajectory).

F0128 14:04:08.248204 32214 problem_impl.cc:635] Parameter block not found: 0x7f67e0035b80. You must add the parameter block to the problem before you can set a lower bound on one of its components.
[FATAL] [1611839048.248835927][/cartographer/cartographer_node][/home/jonathan/cartographer_ws/src/cartographer_ros/cartographer_ros/cartographer_ros/ros_log_sink.cc:63]: F0128 14:04:08.000000 32214 problem_impl.cc:635] 
Parameter block not found: 0x7f67e0035b80.
 You must add the parameter block to the problem before you can set a lower bound on one of its components.

When I called delete onto a frozen trajectory nothing seemed to happen. Is that expected because there are still active constraints between the trajectories?
Side node; I tested this in pure localization mode, while the robot was not localized with respect to the frozen trajectory

[MichaelGrupp]

Will address your points at some later point and let you know, I currently don't have too much time for this.

[Wang-Bo-xuan]

When deleting the same submaps of multiple trajectories, because the reference number is not checked in the pose graph, repeated delete will cause the program to crash.