1. A method executed in a three-dimensional video system, the method comprising: receiving input data associated with a motion vector or disparity vector of a current block; receiving depth values of depth samples in a depth block corresponding to the current block: using a unified derivation method to derive a unified disparity vector from the depth block corresponding to the current block, wherein the unified derivation method generates the unified disparity vector from a subset of the depth samples in the depth block, and wherein the unified disparity vector is generated from at least one of: four corner samples of the depth block: a maximum depth value of said four corner samples of the depth block: or one of: a maximum value, an average value, a median value, a most frequent occurrence, and a linear combination of depth values of a depth sample subset of the depth block; and decoding the input data using said unified disparity vector in Inter mode, Skip mode, or Direct mode, by: using said unified disparity vector to derive an inter-view motion vector or disparity candidate for the current block coded in the Skip mode or the Direct mode, where no residual signal and no motion information is transmitted in the Skip mode and no motion information is transmitted in the Direct mode; and using said unified disparity vector as a motion vector predictor in the Inter mode.