
Im trying to detect a car or human entering my drive way. This is surprisingly difficult. Because I have to ignore anything driving on the road, so I created this zone:

I want to trigger on any object entering that zone from the road. But a car that actually enters my driveway, especially a large van, will also cover the road. The center of the object may even be "on" the road if its a tall delivery van or truck, or a human close to the camera. So this does not trigger:

If I disable the zone crossing requirement, I need to set a really small object size to fit in the narrow (vertical) zone that is not overlapping with the road, and as a result cats and birds and whatever will cause false alarms.
What would help tremendously is having an option to take only the bottom or bottom 20% of the object in to account to determine if something crosses a zone. I could then use a large object size and trigger on (the bottom, ie wheels) crossing my driveway zone. This could also help in general to determine if a human walks on the road or on the driveway, regardless if he is closer or further away.
Less trivial to implement, but possibly useful would be to make BI aware of world geometry. With that I mean, allow us to configure how the ground plane is oriented in the camera view. That way, you could say: detect objects larger than say 1 meter instead of x pixels, and it could work regardless if the object is in the distance or closer to the camera. At least if you assume the bottom of the object touches the ground (not gonna help with spiders and insects).
An illustration:

I would like to detect humans near my shed, but those would be smaller in pixels than a cat in the foreground. Its not trivial to make this work in BI right now, its doable I think with cloning the camera and creating 2 or 3 sets of zones and triggers, but its really clumsy. If BI understood the bottom of the screen is much closer than the top, it could scale the object size trigger accordingly.