Can not find gps velocity?

[libing64]

No description provided.

[yzrobot]

Hi, did you try to run this? If so, when you type $ rostopic echo /vel, you could get something like:

---
header: 
  seq: 6
  stamp: 
    secs: 1531487932
    nsecs: 969429833
  frame_id: "navsat"
twist: 
  linear: 
    x: 7.3565107369
    y: -0.0256791710611
    z: 0.0
  angular: 
    x: 0.0
    y: 0.0
    z: 0.0
---
header: 
  seq: 7
  stamp: 
    secs: 1531487933
    nsecs: 160320017
  frame_id: "navsat"
twist: 
  linear: 
    x: 7.35403464769
    y: 0.192572174502
    z: 0.0
  angular: 
    x: 0.0
    y: 0.0
    z: 0.0

Also c.f. this

[libing64]

@yzrobot Great thanks, so i need the nmea_topic_driver to calclulate gps velocity from nmea_sentence, right?
I would have a try.