# Question on Sentinel Body Frame Origin

Source: https://forum.modalai.com/topic/2374/question-on-sentinel-body-frame-origin
Category: Development Drones (https://forum.modalai.com/category/44/development-drones)
Tags: sentinel
Posted: 2023-07-05 14:06:52 UTC by jmltt
Replies: 2 · Views: 518

## jmltt · 2023-07-05 14:06:52 UTC

I'm trying to set up a mocap system for the source of EV position estimates for the Sentinel.  I'm assuming I need to align the rigid body pivot point generated by the mocap system with the origin of the body frame used by the EKF.  

I was wondering if anyone knew what the best way to tie the body frame origin to a physical location on the Sentinel was.  I was thinking I should use the EKF2_IMU_POS_X/Y/Z parameters, but I wasn't sure which of the two IMUs that parameter is pointing to.

Does anyone know which IMU is being referenced by the EKF2_IMU_POS parameters and would that be the best way of identifying the body frame origin w/rt a physical location or is there a better way to accomplish that?

Thanks

## Reply by Chad Sweet (ModalAI staff) · 2023-07-05 15:33:37 UTC

You can see the extrinsics measurements in /etc/modalai/extrinsics.conf

## Reply by jmltt · 2023-07-05 16:09:47 UTC (in reply to Chad Sweet)

@Chad-Sweet That clears it up, thanks!