More standard sensor interfaces

[mikepurvis]

IMU topics are /imu/data and optionally /imu/mag, in the imu_link frame.

GPS topics are /navsat/fix and optionally /navsat/sentence, /navsat/vel, with the antenna attached to navsat_link.

Cameras as well.

[wjwwood]

I appreciate the initiative to get the ball rolling on this issue. However, I don't have time to push on it right now, so if we want these new standardized interfaces then interested parties in the community should push on this issue, and I'll do my best to arbitrate the process.

I think that in order to do this we will need to come up with a REP, or at least reference an existing REP, for the justification of the new capability interface's contents. Also, it would be best to provide a pull request with the new interface so that there is something to iterate on (once it gets to that point). I would also guess that one pull request per new interface should work best, but I'm not 100% sure of this.

Anyone else have thoughts on the process?

[mikepurvis]

The main points of contention I would see are:

• The type of /imu/mag. Present drivers (um6, microstrain) publish this topic as Vector3Stamped, but they predate the introduction of MagneticField, but I think the REP and capability should specify that, with an intention to migrate drivers and consumers for Jade. @mintar, @chadrockey, do you guys have feelings on this as maintainers of IMU drivers and related software?
• The namespace for GPS receiver messages, as some packages assume /gps. Clearpath has been shipping /navsat for the past year or so, and we're certainly the highest-volume manufacturer of ROS-native outdoor platforms. @ericperko, thoughts on this? Would you entertain switching nmea_navsat_driver to match this for Jade?

[mintar]

+1 for specifying MagneticField as the type of /imu/mag. Also +1 for the IMU topic names.

[ericperko]

Are the only changes for nmea_navsat_driver for this to switch from nmea_sentence to sentence and the default frame_id to navsat_link? If so, I don't see a problem.

[mikepurvis]

Oh, I'm fine for it to remain nmea_sentence; that was just an error in my recollection of what nmea_navsat_driver actually does.