I'm sorry, which application is this in reference to?  In most modelling apps, you could simply scale the "ground" plane up to the point where it seems to touch the horizon from the perspective view, or your could use an environment dome, which contains the background image or sky image, and then scale the ground plane to intersect the environment dome, which would make it appear to extend to the horizon.  Some apps actually have an "infinite" plane, which would extend indefinitely in the render, even if it doesn't appear so in the viewport.  So, it would depend on the application as to how you could handle this.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.