time field "t"

[anath93]

I apologize if this answered before, but just trying to understand concept so I can use this in SLAM instead of going tf2 way, is this field ("t") offset from header.stamp.nanoseconds based on the current time stamp of lidar firing or how is this calculated ?

[Samahu]

Hi @anath93, t refers to the time of firing relative to the beginning of the frame. Refer to this discussion for more details: #206

[anath93]

@Samahu Thank you for replying, I did review that #206, can we say current_t = header.stamp.timestamp[0] - current_frame_firing_time in nanoseconds ?

[Samahu]

point_fire_time_ts(absolute) = header.stamp.timestamp[0] + t

[anath93]

Apologies if I am repeating, "" point_fire_time_ts(absolute) - header.stamp.timestamp[0] = t "" ? I am trying to find "t" equation, meaning how it is calculated in the SDK today and getting printed in PCL2 side.

[Samahu]

Please refer to the line:

ouster-ros/src/os_ros.cpp

Line 213 in 6a7693c

auto ts = timestamp[v_shift]; ts = ts > scan_ts ? ts - scan_ts : 0UL;

which is pretty much the same as: t = point_fire_time_ts(absolute) - header.stamp.timestamp[0]

[anath93]

Thank you !