# Weird Allan-Variance Plot for Gygroscope | ZED X

**URL:** <https://community.stereolabs.com/t/weird-allan-variance-plot-for-gygroscope-zed-x/11811>\
**Category:** ZED X\
**Tags:** ros2\
**Created:** [October 23, 2026, 1:19pm UTC](https://community.stereolabs.com/t/weird-allan-variance-plot-for-gygroscope-zed-x/11811 "2026-10-23T13:19:48Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![j3r3](https://community.stereolabs.com/user_avatar/community.stereolabs.com/j3r3/32/6551_2.png) [@j3r3](https://community.stereolabs.com/u/j3r3)\
**Post date:** [October 23, 2026, 1:19pm UTC](https://community.stereolabs.com/t/weird-allan-variance-plot-for-gygroscope-zed-x/11811/1 "2026-10-23T13:19:48Z")

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Dear all,

I did an Allan-Variance analysis on my ZED X internal raw IMU stream. I recorded IMU measurements via ROS2 for 11.5 hours with a sampling and publising rate of 200Hz. I used the **[allan\_variance\_ros](https://github.com/ori-drs/allan_variance_ros/tree/master)** tool and followed all their steps. However, my gyroscope allan⁻variance plot shows a very weird behavior:

 ![image](https://community.stereolabs.com/uploads/default/original/2X/1/17590f3ce01f7e36fbae39e8d89a1084ffc56868.jpeg)

There is basically no bias-instability and no random walk observable. Therefore, I get a really low random walk result of 9.15e-8. This is suspicious.

I am wondering if the raw IMU measurement still does some bias or drift correction over time. Or what else could be the cause?

I am looking forward to your answers and the discussion.

Best regards,

j3r3

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**Author:** ![Myzhar](https://community.stereolabs.com/user_avatar/community.stereolabs.com/myzhar/32/11_2.png) [@Myzhar](https://community.stereolabs.com/u/Myzhar)\
**Post date:** [October 23, 2026, 3:56pm UTC](https://community.stereolabs.com/t/weird-allan-variance-plot-for-gygroscope-zed-x/11811/2 "2026-10-23T15:56:06Z")

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Hi,

> [@j3r3](#):
>
> I am wondering if the raw IMU measurement still does some bias or drift correction over time. Or what else could be the cause?

The `imu/data_raw` topic published by the [ZED ROS 2 Wrapper](https://github.com/stereolabs/zed-ros2-wrapper) is “raw” only in the sense that it is not orientation-filtered. Its angular velocity is the ZED SDK `angular_velocity` field, which is already corrected for bias, scale, and misalignment, and the gyroscope bias is estimated continuously at runtime. That online bias compensation removes the low-frequency content of the signal, so the bias instability and rate random walk regions flatten out in the Allan deviation plot. This explains the very low random walk value you obtained.

To characterize the sensor itself, record the `angular_velocity_uncalibrated` and `linear_acceleration_uncalibrated` fields directly with the ZED SDK API ([IMUData reference](https://www.stereolabs.com/docs/api/python/classpyzed_1_1sl_1_1IMUData.html)). Call `getSensorsData` with `TIME_REFERENCE::CURRENT` in a dedicated loop, and discard duplicate samples by checking the IMU timestamp. Then run `allan_variance_ros` on that dataset as you did before. Keep the camera still and at a stable temperature for the whole recording.

You can find more information about the [ZED X](https://www.stereolabs.com/products/zed-x) on the [StereoLabs](http://www.stereolabs.com) website.

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<div class="post-metadata">

**Author:** ![j3r3](https://community.stereolabs.com/user_avatar/community.stereolabs.com/j3r3/32/6551_2.png) [@j3r3](https://community.stereolabs.com/u/j3r3)\
**Post date:** [October 24, 2026, 8:37am UTC](https://community.stereolabs.com/t/weird-allan-variance-plot-for-gygroscope-zed-x/11811/3 "2026-10-24T08:37:52Z")

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Thank you for your answer and clarification.

Are there plans in the future to add the true raw gyroscope output in the ROS2 wrapper?

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<div class="post-metadata">

**Author:** ![Myzhar](https://community.stereolabs.com/user_avatar/community.stereolabs.com/myzhar/32/11_2.png) [@Myzhar](https://community.stereolabs.com/u/Myzhar)\
**Post date:** [October 26, 2026, 10:05am UTC](https://community.stereolabs.com/t/weird-allan-variance-plot-for-gygroscope-zed-x/11811/4 "2026-10-26T10:05:42Z")

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> [@j3r3](#):
>
> Are there plans in the future to add the true raw gyroscope output in the ROS2 wrapper?

Normally this is already the case:

> <https://github.com/stereolabs/zed-ros2-wrapper/blob/master/zed_components/src/zed_camera/src/zed_camera_component_main.cpp#L6075-L6135>