[cob_sick_s300] fix fields parameter and handling.

[mgruhler]

Currently, there is was (commented out in #317) a warning about using the fields parameter, as this is the way to go.

"No params for the Sick S300 fieldset were specified --> will using default, but it's deprecated now, please adjust parameters!!!"

However, this is not properly implemented. The driver only supports one field, which defeates the purpose of this parameter. Also, this parameter is nowhere documented.

EDIT answering @ipa-fxm's question below

To be set in the laser yamls (e.g. here)
Old config (without fields param):

"New" config (with fields param and quite some trial-and-error):

fields:
  "1":
    start_angle: -0.75
    stop_angle: 0.0
    scale: 1.0
  "2":
    start_angle: 0.0
    stop_angle: 0.75
    scale: 1.0

What needs to be done:

• check that the max scan fields is 5 in this file.
• check the numbering in the params in this file
• this getScan function seems to only handle the last / one field. However, all configured fields come in one telegram.
• the retrieved fields (which can be arbitrary ranges within [-135°, 135°] without overlaps but with gaps) need to be combined correctly to in the publishLaserScan function which is not done as well.

All in all, my guess is this feature has been implemented without any tests, has never been used, and probably is even unnecessary.

Implementing this correctly would lead to a full driver covering much of the possibilities of the scanner. However, in ROS, this is imo not required. We can easily get the fields we want without having to configure the scanner by using the cob_scan_filter (or, prefereably, the laser_filters).

[fmessmer]

Can someone post what the old config looked like (and where it needs to be set) and what the new config looks like (and where it needs to be set)?

Also, I'd appreciate a few detailed bullet points about what needs to be done implementation-wise to fully implement this feature (and where)

[mgruhler]

@ipa-fxm see edit above.