Frame Question

[james6581]

I have a T265 installed on the drone with the USB port to the left and downfacing, as shown below：

So I set roll, pitch, yaw and gamma as described in t265_tf_to_mavros.launch
r = 3.1415926, p = -1.5707963, y = 0, gamma = -1.5707963，

After I tested the outdoor flight, the position of the uav was stable, but the rotation was not correct from the LOG.
Do you know where the problem might be?

In my understanding, after starting rs_t265, the coordinate system will be initialized according to the current position of t265.
In my case, camera_odom_frame ({W}) will be conform to the right-handed coordinate system, but XYZ is the uav body's back-right-up, not left-forward-up.
This means that every time I start rs_t265, need to place T265 so that camera_odom_frame can generate uav body's left-forward-up?

[thien94]

Hi @james6581,

This is probably because of a known issue with the T265 in down-facing configuration. See here: IntelRealSense/librealsense#4080 (comment)

Essentially, if the T265 boots up when completely pointing downwards, the initial orientation will be unreliable. There is no stable workaround that I know of, so a quick hack is to nose up the vehicle a little bit like this https://files.gitter.im/ArduPilot/VisionProjects/w2Tt/image.png
or use a 45 degree mount instead, similar to this https://user-images.githubusercontent.com/32047382/74317211-9453ff80-4d40-11ea-98e4-f741c8d753de.jpg

Hope this helps.

[james6581]

@thien94
Thank you for your answer. I will try your configuration.
And you mentioned that:

the T265 boots up when completely pointing downwards, the initial orientation will be unreliable.

So if I boots up rs_t265 when t265 facing forward and then turn it facing down, can this issue be avoided?
Or will this issue occur as long as T265 face down?

[thien94]

So if I boots up rs_t265 when t265 facing forward and then turn it facing down, can this issue be avoided?

That's indeed the general idea: Start the T265 in a good working condition (facing forward) then face it down. If the T265 is pointing downwards when it boots up, the issue is likely to occur.