# The problem of optical flow drift

**URL:** <https://discuss.px4.io/t/the-problem-of-optical-flow-drift/34261>\
**Category:** PX4 Autopilot\
**Created:** [September 12, 2023, 3:35am UTC](https://discuss.px4.io/t/the-problem-of-optical-flow-drift/34261 "2023-09-12T03:35:43Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![longwuhen](https://discuss.px4.io/letter_avatar_proxy/v4/letter/l/dec6dc/32.png) [@longwuhen](https://discuss.px4.io/u/longwuhen)\
**Post date:** [September 12, 2023, 3:35am UTC](https://discuss.px4.io/t/the-problem-of-optical-flow-drift/34261/1 "2023-09-12T03:35:43Z")

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Hello everyone. I encountered a problem while debugging optical flow, and look forward to your answer!

The optical flow module I am using is based on the optical flow output calculated by OPENMV, and relevant mavlink messages can be viewed in the optical\_flow\_rad.

What I am puzzled about is that in HITL simulation, the x and y outputs of the optical flow are manually set to 0, but no one has the opportunity to drift in the - y direction. I want to know why