What, exactly, do you mean by "visualization"? A good two dimensional rendering of a 3 dimensional graph should include enough visual information (perspective, etc.) to make the 3 dimensional shape clear. At first I thought you were talking about visualizing a graph when you are only given the formula (say, z= x2+ y2) but, since you say "when graph is plotted on two dimentional sheet which is usually the case", apparently that is not what you are asking.
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