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Hilti-Research / hilti-slam-challenge-2021

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Intended frequency for the ADIS IMU? #12

Open mcamurri opened 3 years ago

mcamurri commented 3 years ago

Hi @hemi86 thanks for organizing this challenge, it is a very exciting opportunity!

I had a look at the ADIS IMU frequency over the logs and it seems a bit jittery.

For example, the uzh_tracking_area_run2.bag holds 73100 messages for a duration of 89s which means an average frequency of ~821 Hz. For Basement_1.bag we have 92360/113 = ~817 Hz.

When running rostopic hz during the log playback I get a fluctuating value between 808 Hz and 830 Hz (I've tried different window sizes as well).

What is the intended frequency for this device? 800 Hz I guess? Is there a particular reason for this jitter?

hemi86 commented 3 years ago

Hi Marco, thank you for raising this issue! The nominal frequency of the ADIS imu is 819.2Hz (according to the dataset). We are currently looking into the jitter that you observed and will get back to you!

Best Michael

bedaberner commented 3 years ago

The "jitter" you see occurs because the IMU messages seem to arrive in batches (same time of arrival,see the following image). Rostopic hz fluctuates, because the in- or exclusion of such a batch makes a big difference. However if you look at the actual timestamps, they are perfectly steady without jitter.

mcamurri commented 3 years ago

Thank you @bedaberner, I have observed the same.

mcamurri commented 3 years ago

Hi Marco, thank you for raising this issue! The nominal frequency of the ADIS imu is 819.2Hz (according to the dataset). We are currently looking into the jitter that you observed and will get back to you!

Best Michael

I see, thanks for the clarification. Because the ADIS IMU is hw syncronised with the alphasense, I expected it to be triggered by the alphasense board at the same (or a fraction) of the alphasense's clock (e.g. 400 or 800 Hz).