Segment Rendering

Hello Everyone! ^^

Well, i’ve watched a video about motion tracking. Setting background and objects etc. So i had this idea that might work, but im not so sure about the results (im really new to Blender/3D editing).
So, its basically like this:

• Lets create a scene and background. For example: A really big hall. Also the camera will move straight forward, maybe 50 seconds from one wall to another.
• Lets Split the scene in a defined numbers of sectors. Lets view inside the hall from one wall to the other. Cutting the floor into 5 pieces, starting with the one thats farthest away from the camera, ending with 5 directly in front of that camera.
• Now Objects. Lets say a Particle system from bottom to top on sector. A lot of small balls just floating in the air.
• Bake the particle system - if necessary.
• Lets render the scene with background, the particles and the camera movements.
• Lets delete Background (and other objects, if any) and moving the (baked) Particles to Sector 2. Turn the Particle Object around by 180° among the z-axis.
• Lets add the rendered movie (containing the background and the animation from sector 1) in the background and run animation again. This time only 40 seconds (After the camera isnt facing any more sectors that are not displayed in the background movie there is no need for additional render). The Goal is obv to overlay the 2nd particle system over the movie.
• Lets move the Particle system to Sector 3 and rotate it again.

Well, you get the idea.

What i think i could be used for:
• Balls could be replaceable with anything that depends mostly on the z-axis, like rain, snow, fragments from a collapsing ceiling, dust, fire, smoke etc.Instead of particle system it also could be used to create a large amount of animated objects. For example installed machines, a hallway of large, animated generators (like vibration, moving/rotating parts), maybe plants, etc.
• A way to split really big scenes so i have a lot of movements and actions in the background i dont have to take care of for my foreground actions (the main reason i came up with this idea).

Flaws:
• All segments have to be rerendered and overlayed again if the background or lighing is changed.
• All sectors has to be rendered to preview the scene.
• Its way harder to add/remove objects and really tricky to move objects through different sectors.
• Will not work with a lot of Lighting settings and shadows, especially dynamic lighting, like a flashlite pointing around, or sun rays through the particles (should be ok as long as light or shadow casts are not moving from one sector to another. However: no indirect lighting unless simulated in the previous sectors)
• Does not work with fluids
• Does not work well with unique looking/shaped objects.

It could still be usefull for large and dark environments like forests, dark industrial stuff, etc and might also works for streets and other things as well. AS i said, main purpose is creating large and complex backgrounds to multiply the averall complexity of particular scenes or to generate a really huge amount of specks, grains, drops etc.

Thats it for now. Any opinions, comments, notes and or criticisms?

(Oh, btw, is there a way to alter the direction of gravity? Or is it fixed to the z-axis?)