1. A method of determining velocity of a target from a moving platform, the method comprising: obtaining, using a radar system, position and radial velocity of the target relative to the moving platform; obtaining, using a vision system, optical flow vectors based on motion of the target relative to the moving platform; estimating a dominant motion vector of the target based on the optical flow vectors; processing, using a processor, the position, the radial velocity, and the dominant motion vector and determining the velocity of the target in two dimensions; and performing, at the moving platform, evasive action based on assessment of a threat of collision posed by the target using the velocity of the target in the two dimensions.