Trigger photo when motion at point.

We have various modes where we can track an object (ie follow me) or POI. What I’d like is sort of the inverse. I typically shoot stills, and would like to pick a point (or box) on the screen and where there is motion in that spot, take the picture. This is my use case. Say I have the drone set in position waiting for action in a specific spot (ie a car or train comes by). It’s rather challenging to do this manually, I typically fire a bit too soon. I’d like to select the spot on the screen, and when the car or train hits that spot, Litchi sees the motion and fires, capturing the image. This removes the variability of how fast/slow my finger is. I know there are risks here, possibly it could be set to only be invoked when the drone is still, and automatically turn off when the drone moves at 1mph or more.