Edge artifacts from scaling large textures

So I applied a large PNG image of a field with trees to a background quad, moved it far back from the camera (perspective) and then scaled it up a bunch to get the right look. However, due to the fact that I don't really know the size of the quad and therefore cannot associate that with the pixel size of the texture and calculate that into the distance from the camera, I of course don't have this scaled pixel perfect.

The image is transparent on top, with a repeating field and trees at the bottom. So the top of the PNG has nothing, while the bottom has the ground. So now in Unity, I have a very faint line at the top of the quad, obviously an artifact from the bottom that is being scaled and tiled.

Changing Filter mode to pixel fixes it, but I get that ugly jittering when the background is moving.

So not sure what my question is, except, maybe, is there a way I can match my quad and background pixel to pixel? If my background is 1920 wide, and my quad is 110 meters from the camera, how much should I scale the quad x ?

Edit: Just found out that increase Aniso Level fixes the line, but still I'd like to know if there's a good to calcualte quad scaling against texture sizes and camera distances.

I know with a sprite you can set the pixels to units, but not with texture.

 

To retain bilinear filtering and fix the bleeding artifacts, you can set your texture to clamp. If your Sprite does not cover the entire texture, then you will need a border around the sprite to prevent these artifacts.

As for figuring out how big something is, try something like http://docs.unity3d.com/Documentation/ScriptReference/Camera.WorldToViewportPoint.html to convert from world space to screen space.