USE optical flow, LIDAR and ZED with TX2

HI.
It is also going to make drones that can be reliably hover in GPS shade areas (in-house or outdoors).

Inside, hovering will be possible through optical flow, Lidar and have actually done this. This is not a problem.
However, I understood through wiki that if I were to float outside using ZED and TX2, I would have to disable EKF2 and activate EKF3.

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If you disable EKF2 according to wiki, isn’t it possible to use everything related to EK2_xx?
Then, I understand that the optical flow and lidar cannot be used either, but am I right?
Finally, I understand that ZED and optical flow and Lidar cannot be used together. Is that right?

If I want to use it with optical flow, lidar can I use ZED and TX2 to hover it without disabling EKF2?

In addition, when using ZED or optical flow, wiki is always set GPS to Disable.
But is it possible to use GPS without disabling and to automatically use optical flow or zed when in shaded areas?