Timestamp delay in dwSensorCamera_getImageNvMedia

Autonomous Machines DRIVE PX2 DriveWorks
#1

Hi,

We are combining data from multiple camera and lidar sources and synchronize the drive px using a gps signal over PTP.

We find that the individual lidars are synchronised very accurately but the cameras appear to have a constant ~20ms time delay.

To get the camera timestamp we are using the dwSensorCamera_getImageNvMedia api and then extract the timestamp from the dwImageNvMedia object.

Our question is whether the timestamp recorded here is the time when the image was originally taken. i.e. as close as possible to when the light hit the sensor or the time when the image was first acquired by the drive-px. If the latter is true, do you know what is the typical time offset between the timestamp recorded and the ‘physical’ image time?

Many thanks,
Jamie

#2

Dear jamie.tattersall,
the timestamping is done when image is acquired by tegra, so there is always a small latency between photon hitting the sensor and we time stamping. However, 20ms seems huge.
Can you let is know your objective and your setup details. Also, can share code snippet to reproduce on our end.
Also when you say 20ms delay, is it w.r.t to timestamp values between lidar and camera?

#3

Hi Siva,

Many thanks for the quick reply and I apologise but I think we may have contacted you prematurely. After a little more investigation we’re coming to the conclusion that the deviations we see probably come from rolling shutter effects.

Many thanks,
Jamie