Hey Neil, I've been playing with zones lately and here's some stuff that I hope might help.
You could try zones like this and see how it works. Let B and C be your zones that detect someone coming from the street/sidewalk toward your porch. Separate them by some space, they don't actually have to be touching. Separate them by more more distance in the area of the frame that is close to the camera and they can be closer together in the area of the frame farther from the camera.
Be sure to have Zone A be the entire scene. Or some other zone, it doesn't matter which one as long as there is a zone that covers everything. I like to have Zone A cover everything and have B and C be my crossing zones.
Your rule will be "B>C" if you only want to detect objects moving toward your porch. If you want it to detect both directions, your rule can be "B-C".
You can also uncheck the "Object Travels (pixels)" checkbox, because you use the distance between the zones for that purpose. That is, an object must travel all the way from the B zone to the C zone to trigger. The cool thing about using zones for this purpose is that you can have different distances in different parts of the scene, just draw your zones so that the distance between them is appropriate for that part of the scene.
Another thing to keep in mind that actually makes things a little harder IMO, is that the zone motion detector uses the
center of each object as the thing that must pass from one zone to another. It's not just that an object touches one zone and then touches another. The reason that makes it a bit more difficult is that the objects change size very quickly, especially shadows, and so the centers move around in somewhat unexpected ways.
Here's an example of B and C zones that could work (very quickly scribbled, you can make them better, like your originals). Notice they're far apart on the left part of the scene which is close to the camera and closer together on the right where the scene is farther away from the camera. HOPEfully this wouldn't trigger for people walking up and down the sidewalk, but would trigger for someone coming up to your porch or driveway. If necessary, you can move C farther away from B to prevent people's shadows from crossing over.
Oh, and another tip I mentioned in another thread is that in the zone editor when you're editing B or C it's hard to see B relative to C (or vice versa) because the one you're not currently editing is the same "dimly shaded" color as A which covers the whole scene. What I like to do before I start editing is first clear A. Then when you edit B or C you can see the other in the dimly shaded color. Then remember before saving to go back to A and click Invert to fill it all back in again. Kind of a lot of steps to go through, but you get used to it.
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